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https://github.com/soapyigu/LeetCode-Swift
Solutions to LeetCode by Swift
https://github.com/soapyigu/LeetCode-Swift
algorithm data-structures interview leetcode swift
Last synced: about 2 months ago
JSON representation
Solutions to LeetCode by Swift
- Host: GitHub
- URL: https://github.com/soapyigu/LeetCode-Swift
- Owner: soapyigu
- License: mit
- Created: 2016-03-31T05:42:24.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2024-02-09T06:09:11.000Z (10 months ago)
- Last Synced: 2024-04-28T20:37:26.534Z (8 months ago)
- Topics: algorithm, data-structures, interview, leetcode, swift
- Language: Swift
- Homepage:
- Size: 12.5 MB
- Stars: 4,789
- Watchers: 166
- Forks: 877
- Open Issues: 39
-
Metadata Files:
- Readme: README.md
- License: License.md
Awesome Lists containing this project
- fucking-awesome-swift - LeetCode-Swift - Solutions to LeetCode interview questions. (Libs / Data Management)
- Awesome-Interview - soapyigu/LeetCode-Swift
- awesome-leetcode - soapyigu/LeetCode-Swift
- awesome-swift - LeetCode-Swift - Solutions to LeetCode interview questions. (Libs / Data Management)
- awesome-swift - LeetCode-Swift - Solutions to LeetCode by Swift ` 📝 a year ago` (Data Management [🔝](#readme))
- awesome-swift - LeetCode-Swift - Solutions to LeetCode interview questions. (Libs / Data Management)
README
# LeetCode by Swift
[LeetCode Online Judge](https://leetcode.com/) is a website containing many **algorithm questions**. Most of them are real interview questions of **Google, Facebook, LinkedIn, Apple**, etc. This repo shows my solutions by Swift with the code style strictly follows the [RayWenderlich Swift Style Guide](https://github.com/raywenderlich/swift-style-guide). Please feel free to reference and **STAR** to support this repo, thank you!
## Progress
[Problem Status](#problem-status) shows the latest progress to all 1000+ questions. Currently we have 400+ completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them.
## Contributors
## Data Structures
* [Array](#array)
* [String](#string)
* [Linked List](#linked-list)
* [Stack](#stack)
* [Queue](#queue)
* [Tree](#tree)
* [Dynamic programming](#dynamic-programming)
* [Depth-first search](#depth-first-search)
* [Breadth-first search](#breadth-first-search)
* [Math](#math)
* [Search](#search)
* [Sort](#sort)
* [Graph](#graph)
* [Design](#design)
## Companies
* [Google](#google)
* [Facebook](#facebook)
* [Snapchat](#snapchat)
* [Uber](#uber)
* [Airbnb](#airbnb)
* [LinkedIn](#linkedin)
* [Amazon](#amazon)
* [Microsoft](#microsoft)
## Array
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Verify an Alien Dictionary](https://leetcode.com/problems/verifying-an-alien-dictionary/)|[Swift](Array/VerifyingAlienDictionary.swift)| Easy| O(n)| O(n)|
[Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/)|[Swift](Array/SortArrayByParity.swift)| Easy| O(n)| O(n)|
[Max Consecutive Ones](https://leetcode.com/problems/max-consecutive-ones/)| [Swift](./Array/MaxConsecutiveOnes.swift)| Easy| O(n)| O(1)|
[Heaters](https://leetcode.com/problems/heaters/)| [Swift](./Array/Heaters.swift)| Easy| O(nlogn)| O(1)|
[Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs/)| [Swift](./Array/NumberBoomerangs.swift)| Easy| O(n ^ 2)| O(n)|
[Island Perimeter](https://leetcode.com/problems/island-perimeter/)| [Swift](./Array/IslandPerimeter.swift)| Easy| O(nm)| O(1)|
[Majority Element](https://leetcode.com/problems/majority-element/)| [Swift](./Array/MajorityElement.swift)| Easy| O(n)| O(1)|
[Majority Element II](https://leetcode.com/problems/majority-element-ii/)| [Swift](./Array/MajorityElementII.swift)| Medium| O(n)| O(1)|
[First Missing Positive](https://leetcode.com/problems/first-missing-positive/)| [Swift](./Array/FirstMissingPositive.swift)| Hard| O(n)| O(n)|
[Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/)| [Swift](./Array/IntersectionTwoArrays.swift)| Easy| O(n)| O(n)|
[Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)| [Swift](./Array/IntersectionTwoArraysII.swift)| Easy| O(n)| O(n)|
[Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)| [Swift](./Array/ContainsDuplicate.swift)| Easy| O(n)| O(n)|
[Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)| [Swift](./Array/ContainsDuplicateII.swift)| Easy| O(n)| O(n)|
[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)| [Swift](./Array/RemoveDuplicatesFromSortedArray.swift)| Easy| O(n)| O(1)|
[Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)| [Swift](./Array/RemoveDuplicatesFromSortedArrayII.swift)| Medium| O(n)| O(1)|
[Move Zeroes](https://leetcode.com/problems/move-zeroes/)| [Swift](./Array/MoveZeroes.swift)| Easy| O(n)| O(1)|
[Remove Element](https://leetcode.com/problems/remove-element/)| [Swift](./Array/RemoveElement.swift)| Easy| O(n)| O(1)|
[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/)| [Swift](./Array/StrobogrammaticNumber.swift)| Easy| O(n)| O(1)|
[Can Place Flowers](https://leetcode.com/problems/can-place-flowers/)| [Swift](./Array/CanPlaceFlowers.swift)| Easy| O(n)| O(1)|
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| O(n)| O(n)|
[Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/)| [Swift](./Array/TwoSumII.swift)| Easy| O(n)| O(1)|
[Two Sum III - Data structure design](https://leetcode.com/problems/two-sum-iii-data-structure-design/)| [Swift](./Array/TwoSumIII.swift)| Easy| O(n)| O(1)|
[Two Sum Less Than K](https://leetcode.com/problems/two-sum-less-than-k/)| [Swift](./Array/TwoSumLessThanK.swift)| Easy| O(nlogn)| O(n)|
[3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
[3Sum Closest](https://leetcode.com/problems/3sum-closest/)| [Swift](./Array/ThreeSumClosest.swift)| Medium| O(n^2)| O(nC3)|
[4Sum](https://leetcode.com/problems/4sum/)| [Swift](./Array/FourSum.swift)| Medium| O(n^3)| O(nC4)|
[Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/)| [Swift](./Array/IncreasingTripletSubsequence.swift)| Medium| O(n)| O(1)|
[Summary Ranges](https://leetcode.com/problems/summary-ranges/)| [Swift](./Array/SummaryRanges.swift)| Medium| O(n)| O(n)|
[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)| [Swift](./Array/NumMatrix.swift)| Medium| O(mn)| O(mn)|
[Missing Ranges](https://leetcode.com/problems/missing-ranges/)| [Swift](./Array/MissingRanges.swift)| Medium| O(n)| O(1)|
[Asteroid Collision](https://leetcode.com/problems/asteroid-collision/)| [Swift](./Array/AsteroidCollision.swift)| Medium| O(n)| O(n)|
[Maximize Distance to Closest Person](https://leetcode.com/problems/maximize-distance-to-closest-person/)| [Swift](./Array/MaximizeDistanceToClosestPerson.swift)| Easy| O(n)| O(1)|
[Exam Room](https://leetcode.com/problems/exam-room/)| [Swift](./Array/ExamRoom.swift)| Medium| O(n)| O(n)|
[Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/)| [Swift](./Array/ShortestWordDistance.swift)| Easy| O(n)| O(1)|
[Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii/)| [Swift](./Array/ShortestWordDistanceII.swift)| Medium| O(n)| O(n)|
[Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/)| [Swift](./Array/ShortestWordDistanceIII.swift)| Medium| O(n)| O(1)|
[Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/)| [Swift](./Array/MinimumSizeSubarraySum.swift)| Medium| O(n)| O(1)|
[Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/)| [Swift](./Array/MaximumSizeSubarraySumEqualsK.swift)| Medium| O(n)| O(n)|
[Smallest Range](https://leetcode.com/problems/smallest-range/)| [Swift](./Array/SmallestRange.swift)| Hard | O(nm)| O(nm)|
[Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)| [Swift](./Array/ProductExceptSelf.swift)| Medium| O(n)| O(1)|
[Rotate Array](https://leetcode.com/problems/rotate-array/)| [Swift](./Array/RotateArray.swift)| Easy| O(n)| O(1)|
[Rotate Image](https://leetcode.com/problems/rotate-image/)| [Swift](./Array/RotateImage.swift)| Medium| O(n^2)| O(1)|
[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)| [Swift](./Array/SpiralMatrix.swift)| Medium| O(n^2)| O(1)|
[Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/)| [Swift](./Array/SpiralMatrixII.swift)| Medium| O(n^2)| O(1)|
[Diagonal Traverse](https://leetcode.com/problems/diagonal-traverse/description/)| [Swift](./Array/DiagonalTraverse.swift)| Medium| O(mn)| O(1)|
[Valid Sudoku](https://leetcode.com/problems/valid-sudoku/)| [Swift](./Array/ValidSudoku.swift)| Easy| O(n^2)| O(n)|
[Set Matrix Zero](https://leetcode.com/problems/set-matrix-zeroes/)| [Swift](./Array/SetMatrixZeroes.swift)| Medium| O(n^2)| O(1)|
[Next Permutation](https://leetcode.com/problems/next-permutation/)| [Swift](./Array/NextPermutation.swift)| Medium| O(n)| O(1)|
[Gas Station](https://leetcode.com/problems/gas-station/)| [Swift](./Array/GasStation.swift)| Medium| O(n)| O(1)|
[Game of Life](https://leetcode.com/problems/game-of-life/)| [Swift](./Array/GameLife.swift)| Medium| O(n)| O(1)|
[Task Scheduler](https://leetcode.com/problems/task-scheduler/)| [Swift](./Array/TaskScheduler.swift)| Medium| O(nlogn)| O(n)|
[Validate IP Address](https://leetcode.com/problems/validate-ip-address/)| [Swift](./Array/ValidateIPAddress.swift)| Medium| O(n)| O(1)|
[Sliding Window Maximum ](https://leetcode.com/problems/sliding-window-maximum/)| [Swift](./Array/SlidingWindowMaximum.swift)| Hard| O(n)| O(n)|
[Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)| [Swift](./Array/LongestConsecutiveSequence.swift)| Hard| O(n)| O(n)|
[Create Maximum Number](https://leetcode.com/problems/create-maximum-number/)| [Swift](./Array/CreateMaximumNumber.swift)| Hard| O(n^2)| O(n)|
[Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/)| [Swift](./Array/FindDisappearedNumbers.swift)| Easy| O(n)| O(1)|
## String
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Fizz Buzz](https://leetcode.com/problems/fizz-buzz/)| [Swift](./String/FizzBuzz.swift)| Easy| O(n)| O(1)|
[First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/)| [Swift](./String/FirstUniqueCharacterInString.swift)| Easy| O(n)| O(1)|
[Keyboard Row](https://leetcode.com/problems/keyboard-row/)| [Swift](./String/KeyboardRow.swift)| Easy| O(nm)| O(n)|
[Valid Word Abbreviation](https://leetcode.com/problems/valid-word-abbreviation/)| [Swift](./String/ValidWordAbbreviation.swift)| Easy| O(n)| O(n)|
[Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)| [Swift](./String/ValidPalindrome.swift)| Easy| O(n)| O(n)|
[Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)| [Swift](./String/ValidPalindromeII.swift)| Easy| O(n)| O(n)|
[Detect Capital](https://leetcode.com/problems/detect-capital/)| [Swift](./String/DetectCapital.swift)| Easy| O(n)| O(1)|
[Count and Say](https://leetcode.com/problems/count-and-say/)| [Swift](./String/CountAndSay.swift)| Easy| O(n^2)| O(1)|
[Flip Game](https://leetcode.com/problems/flip-game/)| [Swift](./String/FlipGame.swift)| Easy| O(n)| O(n)|
[Implement strStr()](https://leetcode.com/problems/implement-strstr/)| [Swift](./String/StrStr.swift)| Easy| O(nm)| O(n)|
[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./String/IsomorphicStrings.swift)| Easy| O(n)| O(n)|
[Reverse String](https://leetcode.com/problems/reverse-string/)| [Swift](./String/ReverseString.swift)| Easy| O(n)| O(n)|
[Reverse String II](https://leetcode.com/problems/reverse-string-ii/)| [Swift](./String/ReverseStringII.swift)| Easy| O(n)| O(n)|
[Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/)| [Swift](./String/ReverseVowelsOfAString.swift)| Easy| O(n)| O(n)|
[Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/)| [Swift](./String/ReverseWordsString.swift)| Medium| O(n)| O(1)|
[Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/)| [Swift](./String/ReverseWordsStringII.swift)| Medium| O(n)| O(1)|
[Reverse Words in a String III](https://leetcode.com/problems/reverse-words-in-a-string-iii/)| [Swift](./String/ReverseWordsStringIII.swift)| Easy| O(n)| O(1)|
[Length of Last Word](https://leetcode.com/problems/length-of-last-word/)| [Swift](./String/AddStrings.swift)| Easy| O(n)| O(n)|
[String Compression](https://leetcode.com/problems/string-compression/)| [Swift](./String/StringCompression.swift)| Easy| O(n)| O(1)|
[Add Strings](https://leetcode.com/problems/add-strings/)| [Swift](./String/LengthLastWord.swift)| Easy| O(n)| O(1)|
[Shortest Distance to a Character](https://leetcode.com/problems/shortest-distance-to-a-character/)| [Swift](./String/ShortestDistanceToACharacter.swift)| Easy| O(n)| O(1)|
[Multiply Strings](https://leetcode.com/problems/multiply-strings/)| [Swift](./String/MultiplyStrings.swift)| Medium| O(n)| O(1)|
[Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation/)| [Swift](./String/PalindromePermutation.swift)| Easy| O(n)| O(n)|
[Valid Anagram](https://leetcode.com/problems/valid-anagram/)| [Swift](./String/ValidAnagram.swift)| Easy| O(n)| O(n)|
[Ransom Note](https://leetcode.com/problems/ransom-note/)| [Swift](./String/RansomNote.swift)| Easy| O(n)| O(n)|
[Group Anagrams](https://leetcode.com/problems/anagrams/)| [Swift](./String/GroupAnagrams.swift)| Medium| O(nmlogm + nlogn)| O(n)
[Find Duplicate File in System](https://leetcode.com/problems/find-duplicate-file-in-system/)| [Swift](./String/FindDuplicateFileInSystem.swift)| Medium| O(nm)| O(n)
[Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)| [Swift](./String/LongestCommonPrefix.swift)| Easy| O(nm)| O(m)|
[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)| [Swift](./String/LongestSubstringWithoutRepeatingCharacters.swift)| Medium| O(n)| O(n)|
[One Edit Distance](https://leetcode.com/problems/one-edit-distance/)| [Swift](./String/OneEditDistance.swift)| Medium| O(n)| O(n)|
[Word Pattern](https://leetcode.com/problems/word-pattern/)| [Swift](./String/WordPattern.swift)| Easy| O(n)| O(n)|
[Permutation in String](https://leetcode.com/problems/permutation-in-string/)| [Swift](/.String/PermutationInString.swift)| Medium| O(nm)| O(n)|
[Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/)| [Swift](/.String/FindAllAnagramsInAString.swift)| Medium| O(n)| O(n)|
[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)| [Swift](./String/MinimumWindowSubstring.swift)| Hard| O(n^2)| O(n)|
[Longest Substring with At Most Two Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/)| [Swift](./String/LongestSubstringMostTwoDistinctCharacters.swift)| Hard| O(n)| O(n)|
[Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)| [Swift](./String/LongestSubstringMostKDistinctCharacters.swift)| Hard| O(n)| O(n)|
[Text Justification](https://leetcode.com/problems/text-justification/)| [Swift](./String/TextJustification.swift)| Hard| O(n)| O(n)|
[Find the Closest Palindrome](https://leetcode.com/problems/find-the-closest-palindrome/)| [Swift](./String/FindClosestPalindrome.swift)| Hard| O(n)| O(n)|
## Linked List
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| O(n)| O(1)|
[Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)| [Swift](./LinkedList/PalindromeLinkedList.swift)| Easy| O(n)| O(1)|
[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)| [Swift](./LinkedList/SwapNodesInPairs.swift)| Easy| O(n)| O(1)|
[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/)| [Swift](./LinkedList/RemoveLinkedListElements.swift)| Easy| O(n)| O(1)|
[Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/)| [Swift](./LinkedList/RemoveDuplicatesFromSortedList.swift)| Easy| O(n)| O(1)|
[Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/)| [Swift](./LinkedList/RemoveDuplicatesFromSortedListII.swift)| Medium| O(n)| O(1)|
[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| [Swift](./LinkedList/RemoveNthFromEnd.swift)| Easy| O(n)| O(1)|
[Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list/)| [Swift](./LinkedList/OddEvenLinkedList.swift)| Medium| O(n)| O(1)|
[Rotate List](https://leetcode.com/problems/rotate-list/)| [Swift](./LinkedList/RotateList.swift)| Medium| O(n)| O(1)|
[Reorder List](https://leetcode.com/problems/reorder-list/)| [Swift](./LinkedList/ReorderList.swift)| Medium| O(n)| O(1)|
[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| [Swift](./LinkedList/MergeTwoSortedLists.swift)| Easy| O(n)| O(1)|
[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)| [Swift](./LinkedList/MergeKSortedLists.swift)| Hard| O(mlogn)| O(1)|
[Partition List](https://leetcode.com/problems/partition-list/)| [Swift](./LinkedList/PartitionList.swift)| Medium| O(n)| O(1)|
[Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/)| [Swift](./LinkedList/ReverseNodesInKGroup.swift)| Hard| O(n)| O(1)|
[LRU Cache](https://leetcode.com/problems/lru-cache/) | [Swift](./LinkedList/LRUCache.swift) | Hard| O(1)| O(1)|
[LFU Cache](https://leetcode.com/problems/lfu-cache/) | [Swift](./LinkedList/LFUCache.swift) | Hard| O(1)| O(1)|
## Stack
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Min Stack](https://leetcode.com/problems/min-stack/)| [Swift](./Stack/MinStack.swift)| Easy| O(1)| O(n)|
[Max Stack](https://leetcode.com/problems/max-stack/)| [Swift](./Stack/MaxStack.swift)| Easy| O(n)| O(n)|
[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [Swift](./Stack/ValidParentheses.swift)| Easy| O(n)| O(n)|
[Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/)| [Swift](./Stack/LongestValidParentheses.swift)| Hard| O(n)| O(n)|
[Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)| [Swift](./Stack/EvaluateReversePolishNotation.swift)| Medium| O(n)| O(n)|
[Exclusive Time of Functions](https://leetcode.com/problems/exclusive-time-of-functions/)| [Swift](./Stack/ExclusiveTimeFunctions.swift) | Medium| O(n)| O(n)|
[Simplify Path](https://leetcode.com/problems/simplify-path/)| [Swift](./Stack/SimplifyPath.swift)| Medium| O(n)| O(n)|
[Remove K Digits](https://leetcode.com/problems/remove-k-digits/)| [Swift](./Stack/RemoveKDigits.swift)| Medium| O(n)| O(n)|
[Ternary Expression Parser](https://leetcode.com/problems/ternary-expression-parser/)| [Swift](./Stack/TernaryExpressionParser.swift)| Medium| O(n)| O(n)|
[Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/)| [Swift](./Stack/PreorderTraversal.swift)| Medium| O(n)| O(n)|
[Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)| [Swift](./Stack/InorderTraversal.swift)| Medium| O(n)| O(n)|
[Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/)| [Swift](./Stack/BinarySearchTreeIterator.swift)| Medium| O(n)| O(n)|
[Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/)| [Swift](./Stack/PostorderTraversal.swift)| Hard| O(n)| O(n)|
[Decode String](https://leetcode.com/problems/decode-string/)| [Swift](./Stack/DecodeString.swift)| Medium| O(n)| O(n)|
[Basic Calculator](https://leetcode.com/problems/basic-calculator/)| [Swift](./Stack/BasicCalculator.swift)| Hard| O(n)| O(n)|
## Queue
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks)| [Swift](./Queue/ImplementQueueUsingStacks.swift)| Easy| O(n)| O(n)|
## Tree
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Same Tree](https://oj.leetcode.com/problems/same-tree/)| [Swift](./Tree/SameTree.swift)| Easy| O(n)| O(n)|
[Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)| [Swift](./Tree/SymmetricTree.swift)| Easy| O(n)| O(n)|
[Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)| [Swift](./Tree/InvertBinaryTree.swift)| Easy| O(n)| O(n)|
[Binary Tree Upside Down](https://leetcode.com/problems/binary-tree-upside-down/)| [Swift](./Tree/BinaryTreeUpsideDown.swift)| Medium| O(n)| O(1)|
[Minimum Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree/)| [Swift](./Tree/MinimumDepthOfBinaryTree.swift)| Easy| O(n)| O(1)|
[Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)| [Swift](./Tree/MaximumDepthOfBinaryTree.swift)| Easy| O(n)| O(1)|
[Diameter of Binary Tree](https://leetcode.com/problems/diameter-of-binary-tree/)| [Swift](./Tree/DiameterBinaryTree.swift)| Easy| O(n)| O(1)|
[Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)| [Swift](./Tree/BalancedBinaryTree.swift)| Easy| O(n)| O(n)|
[Sum of Left Leaves](https://leetcode.com/problems/sum-of-left-leaves/)| [Swift](./Tree/SumLeftLeaves.swift)| Easy| O(n)| O(1)|
[Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)| [Swift](./Tree/FlattenBinaryTreeLinkedList.swift)| Medium| O(n)| O(1)|
[Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/)| [Swift](./Tree/ConvertSortedArrayBinarySearchTree.swift)| Easy| O(n)| O(1)|
[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)| [Swift](./Tree/ValidateBinarySearchTree.swift)| Medium| O(n)| O(log n)|
[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/)| [Swift](./Tree/BinaryTreeLevelOrderTraversal.swift)| Easy| O(n)| O(n)|
[Binary Tree Level Order Traversal II](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/)| [Swift](./Tree/BinaryTreeLevelOrderTraversalII.swift)| Easy| O(n)| O(n)|
[Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/description/) | [Swift](./Tree/MergeTwoBinaryTrees.swift) | Easy | O(n) | O(n) |
[Binary Tree Zigzag Level Order Traversal](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/)| [Swift](./Tree/BinaryTreeZigzagLevelOrderTraversal.swift)| Medium| O(n)| O(n)|
[Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/)| [Swift](./Tree/BinaryTreeVerticalOrderTraversal.swift)| Medium| O(n)| O(n)|
[Kth Smallest Element in a BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/)| [Swift](./Tree/KthSmallestElementBST.swift)| Medium| O(n)| O(n)|
[Binary Tree Right Side View](https://leetcode.com/problems/binary-tree-right-side-view/)| [Swift](./Tree/BinaryTreeRightSideView.swift)| Medium| O(n)| O(n)|
[Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)| [Swift](./Tree/ConstructBinaryTreePreorderInorder.swift)| Medium| O(nlogn)| O(1)|
[Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)| [Swift](./Tree/ConstructBinaryTreeInorderPostorder.swift)| Medium| O(nlogn)| O(1)|
[Path Sum](https://leetcode.com/problems/path-sum/)| [Swift](./Tree/PathSum.swift)| Easy| O(n)| O(n)|
[Path Sum II](https://leetcode.com/problems/path-sum-ii/)| [Swift](./Tree/PathSumII.swift)| Medium| O(n)| O(n)|
[Path Sum III](https://leetcode.com/problems/path-sum-iii/)| [Swift](./Tree/PathSumIII.swift)| Easy| O(n^2)| O(1)|
[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| [Swift](./Tree/BinaryTreePaths.swift)| Easy| O(n)| O(n)|
[Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/)| [Swift](./Tree/BinaryTreeMaximumPathSum.swift)| Hard| O(n)| O(1)|
[House Robber III](https://leetcode.com/problems/house-robber-iii/)| [Swift](./Tree/HouseRobberIII.swift)| Medium| O(n)| O(1)|
[Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees/)| [Swift](./Tree/UniqueBinarySearchTrees.swift)| Medium| O(n^2)| O(n)|
[Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/)| [Swift](./Tree/RecoverBinarySearchTree.swift)| Hard| O(n)| O(1)|
[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)| [Swift](./Tree/SerializeDeserializeBinaryTree.swift)| Hard| O(n)| O(n)|
[Serialize and Deserialize N-ary Tree](https://leetcode.com/problems/serialize-and-deserialize-n-ary-tree/)| [Swift](./Tree/SerializeDeserializeNAryTree.swift)| Hard| O(n)| O(n)|
## Dynamic programming
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Nested List Weight Sum](https://leetcode.com/problems/nested-list-weight-sum/)| [Swift](./DP/NestedListWeightSum.swift)| Easy| O(n)| O(1)|
[Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)| [Swift](./DP/ClimbingStairs.swift)| Easy| O(n)| O(1)|
[Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/)| [Swift](./DP/MinCostClimbingStairs.swift)| Easy| O(n)| O(n)|
[Unique Paths](https://leetcode.com/problems/unique-paths/)| [Swift](./DP/UniquePaths.swift)| Medium| O(mn)| O(mn)|
[Unique Paths II](https://leetcode.com/problems/unique-paths-ii/)| [Swift](./DP/UniquePathsII.swift)| Medium| O(mn)| O(mn)|
[Nested List Weight Sum II](https://leetcode.com/problems/nested-list-weight-sum-ii/)| [Swift](./DP/NestedListWeightSumII.swift)| Medium| O(n)| O(n)|
[Flip Game II](https://leetcode.com/problems/flip-game-ii/)| [Swift](./DP/FlipGameII.swift)| Medium| O(n)| O(n)|
[Can I Win](https://leetcode.com/problems/can-i-win/)| [Swift](./DP/CanIWin.swift)| Medium| O(2^n)| O(n)|
[Decode Ways](https://leetcode.com/problems/decode-ways/)| [Swift](./DP/DecodeWays.swift) | Medium| O(n)|O(n)|
[Minimum Path Sum](https://leetcode.com/problems/minimum-path-sum/)| [Swift](./DP/MinimumPathSum.swift)| Medium| O(mn)| O(mn)|
[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)| [Swift](./DP/GenerateParentheses.swift)| Medium| O(2^n)| O(n)|
[Different Ways to Add Parentheses](https://leetcode.com/problems/different-ways-to-add-parentheses/)| [Swift](./DP/DifferentWaysAddParentheses.swift)| Medium| O(n^n)| O(n)|
[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [Swift](./DP/BestTimeBuySellStock.swift)| Easy| O(n)| O(1)|
[Best Time to Buy and Sell Stock II](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/)| [Swift](./DP/BestTimeBuySellStockII.swift)| Medium| O(n)| O(1)|
[Best Time to Buy and Sell Stock III](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/)| [Swift](./DP/BestTimeBuySellStockIII.swift)| Hard| O(n)| O(n)|
[Best Time to Buy and Sell Stock IV](https://leetcode.com/problems/https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/)| [Swift](./DP/BestTimeBuySellStockIV.swift)| Hard| O(n^2)| O(n)|
[Best Time to Buy and Sell Stock with Cooldown](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/)| [Swift](./DP/BestTimeBuySellStockCooldown.swift)| Medium| O(n^2)| O(n)|
[Maximum Sum of 3 Non-Overlapping Subarrays](https://leetcode.com/problems/maximum-sum-of-3-non-overlapping-subarrays/)| [Swift](./DP/MaximumSumThreeNonOverlappingSubarrays.swift)| Hard| O(n)| O(n)|
[Coin Change](https://leetcode.com/problems/coin-change/)| [Swift](./DP/CoinChange.swift)| Medium| O(n^2)| O(n)|
[Coin Change II](https://leetcode.com/problems/coin-change-ii/)| [Swift](./DP/CoinChangeII.swift)| Medium| O(n^2)| O(n)|
[Paint House](https://leetcode.com/problems/paint-house/)| [Swift](./DP/PaintHouse.swift)| Easy| O(n)| O(n)|
[Paint House II](https://leetcode.com/problems/paint-house-ii/)| [Swift](./DP/PaintHouseII.swift)| Hard| O(n)| O(1)|
[Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)| [Swift](./DP/LongestIncreasingSubsequence.swift)| Medium| O(nlogn)| O(n)|
[Longest Common Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)| [Swift](./DP/LongestCommonSubsequence.swift)| Medium| O(mn)| O(1)|
[Palindromic Substrings](https://leetcode.com/problems/palindromic-substrings/)| [Swift](./DP/PalindromicSubstrings.swift)| Medium| O(n^2)| O(n^2)|
[Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)| [Swift](./DP/LongestPalindromicSubstring.swift)| Medium| O(n^2)| O(n^2)|
[Perfect Squares](https://leetcode.com/problems/perfect-squares/)| [Swift](./DP/PerfectSquares.swift)| Medium| O(n^2)| O(n)|
[House Robber](https://leetcode.com/problems/house-robber/)| [Swift](./DP/HouseRobber.swift)| Easy| O(n)| O(1)|
[House Robber II](https://leetcode.com/problems/house-robber-ii/)| [Swift](./DP/HouseRobberII.swift)| Medium| O(n)| O(1)|
[Paint Fence](https://leetcode.com/problems/paint-fence/)| [Swift](./DP/PaintFence.swift)| Easy| O(n)| O(n)|
[Maximum Subarray](https://leetcode.com/problems/maximum-subarray/)| [Swift](./DP/MaximumSubarray.swift)| Medium| O(n)| O(1)|
[Maximum Product Subarray](https://leetcode.com/problems/maximum-product-subarray/)| [Swift](./DP/MaximumProductSubarray.swift)| Medium| O(n)| O(1)|
[Maximum Number of Points with Cost](https://leetcode.com/problems/maximum-number-of-points-with-cost/)| [Swift](./DP/MaximumNumberPointsCost.swift)| Medium| O(mn)| O(1)|
[Maximal Square](https://leetcode.com/problems/maximal-square/)| [Swift](./DP/MaximalSquare.swift)| Medium| O(mn)| O(mn)|
[Edit Distance](https://leetcode.com/problems/edit-distance/)| [Swift](./DP/EditDistance.swift)| Hard| O(mn)| O(mn)|
[Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/)| [Swift](./DP/CombinationSumIV.swift)| Medium| O(2^n)| O(n)|
[Triangle](https://leetcode.com/problems/triangle/)| [Swift](./DP/Triangle.swift)| Medium| O(2^n)| O(m)|
[Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/)| [Swift](./DP/WiggleSubsequence.swift)| Medium| O(n)| O(1)|
[Wildcard Matching](https://leetcode.com/problems/wildcard-matching/)| [Swift](./DP/WildcardMatching.swift)| Hard| O(mn)| O(mn)|
[Regular Expression Matching](https://leetcode.com/problems/regular-expression-matching/)| [Swift](./DP/RegularExpressionMatching.swift)| Hard| O(mn)| O(mn)|
[Minimum Window Subsequence](https://leetcode.com/problems/minimum-window-subsequence/)| [Swift](./DP/MinimumWindowSubsequence.swift)| Hard| O(mn)| O(mn)|
[Guess Number Higher or Lower II](https://leetcode.com/problems/guess-number-higher-or-lower-ii/)| [Swift](./DP/GuessNumberHigherOrLowerII.swift)| Medium| O(nlogn)| O(n^2)|
[Burst Ballons](https://leetcode.com/problems/burst-balloons/)| [Swift](./DP/BurstBalloons.swift)| Hard| O(n^3)| O(n)|
[Frog Jump](https://leetcode.com/problems/frog-jump/)| [Swift](./DP/FrogJump.swift)| Hard| O(n^2)| O(n)|
[Jump Game](https://leetcode.com/problems/jump-game/)| [Swift](./DP/JumpGame.swift)| Medium| O(n)| O(1)|
[Dungeon Game](https://leetcode.com/problems/dungeon-game/)| [Swift](./DP/DungeonGame.swift)| Hard| O(nm)| O(nm)|
## Depth-first search
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Permutations](https://leetcode.com/problems/permutations/)| [Swift](./DFS/Permutations.swift)| Medium| O(2^n)| O(n)|
[Permutations II](https://leetcode.com/problems/permutations-ii/)| [Swift](./DFS/PermutationsII.swift)| Medium| O(2^n)| O(n)|
[Subsets](https://leetcode.com/problems/subsets/)| [Swift](./DFS/Subsets.swift)| Medium| O(n^n)| O(n)|
[Subsets II](https://leetcode.com/problems/subsets-ii/)| [Swift](./DFS/SubsetsII.swift)| Medium| O(2^n)| O(n)|
[Combinations](https://leetcode.com/problems/combinations/)| [Swift](./DFS/Combinations.swift)| Medium| O(2^n)| O(n)|
[Combination Sum](https://leetcode.com/problems/combination-sum/)| [Swift](./DFS/CombinationSum.swift)| Medium| O(2^n)| O(n)|
[Combination Sum II](https://leetcode.com/problems/combination-sum-ii/)| [Swift](./DFS/CombinationSumII.swift)| Medium| O(2^n)| O(n)|
[Combination Sum III](https://leetcode.com/problems/combination-sum-iii/)| [Swift](./DFS/CombinationSumIII.swift)| Medium| O(2^n)| O(n)|
[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| O(4^n)| O(n)|
[Factor Combinations](https://leetcode.com/problems/factor-combinations/)| [Swift](./DFS/FactorCombinations.swift)| Medium| O(n^n))| O(2^n - 1)|
[Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii/)| [Swift](./DFS/StrobogrammaticNumberII.swift)| Medium| O(m^n)| O(n)|
[Generalized Abbreviation](https://leetcode.com/problems/generalized-abbreviation/)| [Swift](./DFS/GeneralizedAbbreviation.swift)| Medium| O(n^n)| O(2^n)|
[Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning/)| [Swift](./DFS/PalindromePartitioning.swift)| Medium| O(n^n)| O(n)|
[Is Graph Bipartite](https://leetcode.com/problems/is-graph-bipartite/)| [Swift](./DFS/IsGraphBipartite.swift)| Medium| O(n)| O(n)|
[Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Swift](./DFS/NumberofIslands.swift)| Medium| O((mn)^2)| O(1)|
[Walls and Gates](https://leetcode.com/problems/walls-and-gates/)| [Swift](./DFS/WallsGates.swift)| Medium| O(n^n)| O(2^n)|
[Word Search](https://leetcode.com/problems/word-search/)| [Swift](./DFS/WordSearch.swift)| Medium| O((mn * 4 ^ (k - 1))| O(mn)|
[Word Search II](https://leetcode.com/problems/word-search-ii/)| [Swift](./DFS/WordSearchII.swift)| Hard| O(((mn)^2))| O(n^2)|
[Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/)| [Swift](./DFS/WordDictionary.swift)| Medium| O(n)| O(n)|
[Partition to K Equal Sum Subsets](https://leetcode.com/problems/partition-to-k-equal-sum-subsets/)| [Swift](./DFS/PartitionKEqualSumSubsets.swift)| Medium| O(k^n)| O(n)|
[N-Queens](https://leetcode.com/problems/n-queens/)| [Swift](./DFS/NQueens.swift)| Hard| O((n^n))| O(n^2)|
[N-Queens II](https://leetcode.com/problems/n-queens-ii/)| [Swift](./DFS/NQueensII.swift)| Hard| O((n^n))| O(n)|
[Word Squares](https://leetcode.com/problems/word-squares/)| [Swift](./DFS/WordSquares.swift)| Hard| O((n^2))| O(n^2)|
[Word Pattern II](https://leetcode.com/problems/word-pattern-ii/)| [Swift](./DFS/WordPatternII.swift)| Hard| O(n^n)| O(n)|
[Sudoku Solver](https://leetcode.com/problems/sudoku-solver/)| [Swift](./DFS/SudokuSolver.swift)| Hard| O(n^4)| O(1)|
[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)| [Swift](./DFS/RemoveInvalidParentheses.swift)| Hard| O(n^n)| O(n)|
[Expression Add Operators](https://leetcode.com/problems/expression-add-operators/)| [Swift](./DFS/ExpressionAddOperators.swift)| Hard| O(n^n)| O(n)|
## Breadth-first search
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Word Ladder](https://leetcode.com/problems/word-ladder/)| [Swift](./BFS/WordLadder.swift)| Medium| O(nm)| O(nm)|
[Evaluate Division](https://leetcode.com/problems/evaluate-division/)| [Swift](./BFS/EvaluateDivision.swift)| Medium| O(n^2)| O(n)|
[Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)| [Swift](./BFS/ShortestDistanceAllBuildings.swift)| Hard| O((mn)^2)| O(mn)|
## Math
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Add Binary](https://leetcode.com/problems/add-binary/)| [Swift](./Math/AddBinary.swift)| Easy| O(n)| O(n)|
[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)| [Swift](./Math/AddTwoNumbers.swift)| Medium| O(n)| O(1)|
[Add Digits](https://leetcode.com/problems/add-digits/)| [Swift](./Math/AddDigits.swift)| Easy| O(1)| O(1)|
[Plus One](https://leetcode.com/problems/plus-one/)| [Swift](./Math/PlusOne.swift)| Easy| O(n)| O(1)|
[Missing Number](https://leetcode.com/problems/missing-number/)| [Swift](./Math/MissingNumber.swift)| Easy| O(n)| O(1)|
[Divide Two Integers](https://leetcode.com/problems/divide-two-integers/)| [Swift](./Math/DivideTwoIntegers.swift)| Medium| O(logn)| O(1)|
[Number Complement](https://leetcode.com/problems/number-complement/)| [Swift](./Math/NumberComplement.swift)| Easy| O(n)| O(1)|
[Hamming Distance](https://leetcode.com/problems/hamming-distance/)| [Swift](./Math/HammingDistance.swift)| Easy| O(n)| O(1)|
[Integer Break](https://leetcode.com/problems/integer-break/)| [Swift](./Math/IntegerBreak.swift)| Medium| O(logn)| O(1)|
[Factorial Trailing Zeroes](https://leetcode.com/problems/factorial-trailing-zeroes/)| [Swift](./Math/FactorialTrailingZeroes.swift)| Medium | O(logn)| O(1)|
[Happy Number](https://leetcode.com/problems/happy-number/)| [Swift](./Math/HappyNumber.swift)| Easy| O(n)| O(n)|
[Single Number](https://leetcode.com/problems/single-number/)| [Swift](./Math/SingleNumber.swift)| Medium| O(n)| O(1)|
[Ugly Number](https://leetcode.com/problems/ugly-number/)| [Swift](./Math/UglyNumber.swift)| Easy| O(logn)| O(1)|
[Ugly Number II](https://leetcode.com/problems/ugly-number-ii/)| [Swift](./Math/UglyNumberII.swift)| Medium| O(n)| O(n)|
[Super Ugly Number](https://leetcode.com/problems/super-ugly-number/)| [Swift](./Math/SuperUglyNumber.swift)| Medium| O(n^2)| O(n)|
[Count Primes](https://leetcode.com/problems/count-primes/)| [Swift](./Math/CountPrimes.swift)| Easy| O(n)| O(n)|
[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)| [Swift](./Math/Atoi.swift)| Easy| O(n)| O(1)|
[Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/)| [Swift](./Math/FractionToRecurringDecimal.swift) | Medium| O(logn)| O(n)|
[Pow(x, n)](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./Math/Pow.swift)| Medium| O(logn)| O(1)|
[Power of Two](https://leetcode.com/problems/power-of-two/)| [Swift](./Math/PowerTwo.swift)| Easy| O(1)| O(1)|
[Power of Three](https://leetcode.com/problems/power-of-three/)| [Swift](./Math/PowerThree.swift)| Easy| O(1)| O(1)|
[Super Power](https://leetcode.com/problems/super-pow/)| [Swift](./Math/SuperPow.swift)| Medium| O(n)| O(1)|
[Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/)| [Swift](./Math/SumTwoIntegers.swift)| Easy| O(n)| O(1)|
[Reverse Integer](https://leetcode.com/problems/reverse-integer/)| [Swift](./Math/ReverseInteger.swift)| Easy| O(n)| O(1)|
[Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/)| [Swift](./Math/ExcelSheetColumnNumber.swift)| Easy| O(n)| O(1)|
[Integer to Roman](https://leetcode.com/problems/integer-to-roman/)| [Swift](./Math/IntegerToRoman.swift)| Medium| O(n)| O(1)|
[Roman to Integer](https://leetcode.com/problems/roman-to-integer/)| [Swift](./Math/RomanToInteger.swift)| Easy| O(n)| O(n)|
[Integer to English Words](https://leetcode.com/problems/integer-to-english-words/)| [Swift](./Math/IntegerEnglishWords.swift)| Hard| O(n)| O(1)|
[Sparse Matrix Multiplication](https://leetcode.com/problems/sparse-matrix-multiplication/)| [Swift](./Math/SparseMatrixMultiplication.swift)| Medium| O(n^3)| O(n^2)|
[Rectangle Area](https://leetcode.com/problems/rectangle-area/)| [Swift](./Math/RectangleArea.swift)| Easy| O(1)| O(1)|
[Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-moves-to-equal-array-elements/)| [Swift](./Math/MinimumMovesEqualArrayElements.swift)| Easy| O(n)| O(1)|
[Pour Water](https://leetcode.com/problems/pour-water/)| [Swift](./Math/TrappingRainWater.swift)| Hard| O(n)| O(n)|
[Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)| [Swift](./Math/TrappingRainWater.swift)| Medium| O(nk)| O(1)|
[Container With Most Water](https://leetcode.com/problems/container-with-most-water/)| [Swift](./Math/ContainerMostWater.swift)| Medium| O(n)| O(1)|
[Counting Bits](https://leetcode.com/problems/counting-bits/)| [Swift](./Math/CountingBits.swift)| Medium| O(n)| O(n)|
[K-th Smallest in Lexicographical Order](https://leetcode.com/problems/k-th-smallest-in-lexicographical-order/)| [Swift](./Math/KthSmallestLexicographicalOrder.swift)| Hard| O(n)| O(1)|
[Gary Code](https://leetcode.com/problems/gray-code/)| [Swift](./Math/GaryCode.swift)| Medium| O(n)| O(2^n)|
[Permutation Sequence](https://leetcode.com/problems/permutation-sequence/)| [Swift](./Math/PermutationSequence.swift)| Medium| O(n^2)| O(1)|
[Line Reflection](https://leetcode.com/problems/line-reflection/)| [Swift](./Math/LineReflection.swift)| Medium| O(n)| O(n)|
[Valid Number](https://leetcode.com/problems/valid-number/)| [Swift](./Math/ValidNumber.swift)| Hard| O(n)| O(1)|
## Search
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Closest Binary Search Tree Value](https://leetcode.com/problems/closest-binary-search-tree-value/)| [Swift](./Search/ClosestBinarySearchTreeValue.swift)| Easy| O(logn)| O(1)|
[Closest Binary Search Tree Value II](https://leetcode.com/problems/closest-binary-search-tree-value-ii/)| [Swift](./Search/ClosestBinarySearchTreeValueII.swift)| Hard| O(n)| O(n)|
[Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/)| [Swift](./Search/SearchInRotatedSortedArray.swift)| Hard| O(logn)| O(1)|
[Search in Rotated Sorted Array II](https://leetcode.com/problems/search-in-rotated-sorted-array-ii/)| [Swift](./Search/SearchInRotatedSortedArrayII.swift)| Medium| O(logn)| O(1)|
[Find Minimum in Rotated Sorted Array](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/)| [Swift](./Search/FindMinimumRotatedSortedArray.swift)| Medium| O(logn)| O(1)|
[Find Minimum in Rotated Sorted Array II](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii/)| [Swift](./Search/FindMinimumRotatedSortedArrayII.swift)| Hard| O(logn)| O(1)|
[Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)| [Swift](./Search/Search2DMatrix.swift)| Medium| O(log(m + n))| O(1)|
[Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/)| [Swift](./Search/Search2DMatrixII.swift)| Medium| O(m + n)| O(1)|
[Search for a Range](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/)| [Swift](./Search/SearchForARange.swift)| Medium| O(logn)| O(1)|
[Search Insert Position](https://leetcode.com/problems/search-insert-position/)| [Swift](./Search/SearchInsertPosition.swift)| Medium| O(logn)| O(1)|
[Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/)| [Swift](./Search/PeakIndexMountainArray.swift)| Easy| O(logn)| O(1)|
[Find Peak Element](https://leetcode.com/problems/find-peak-element/)| [Swift](./Search/FindPeakElement.swift)| Medium| O(logn)| O(1)|
[Random Pick with Weight](https://leetcode.com/problems/random-pick-with-weight/)| [Swift](./Search/RandomPickWeight.swift)| Medium| O(logn)| O(1)|
[Sqrt(x)](https://leetcode.com/problems/sqrtx/)| [Swift](./Search/Sqrtx.swift)| Medium| O(logn)| O(1)|
[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)| [Swift](./Search/MedianTwoSortedArrays.swift)| Hard| O(log(m + n))| O(1)|
[Minimize Max Distance to Gas Station](https://leetcode.com/problems/minimize-max-distance-to-gas-station/)| [Swift](./Search/MinimizeMaxDistanceGasStation.swift)| Hard| O(nlogm)| O(1)|
## Sort
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array/)| [Swift](./Sort/MergeSortedArray.swift)| Easy| O(n)| O(1)|
[Sort Colors](https://leetcode.com/problems/sort-colors/)| [Swift](./Sort/SortColors.swift)| Medium| O(n)| O(1)|
[Wiggle Sort](https://leetcode.com/problems/wiggle-sort/)| [Swift](./Sort/WiggleSort.swift)| Medium| O(n)| O(1)|
[Wiggle Sort II](https://leetcode.com/problems/wiggle-sort-ii/)| [Swift](./Sort/WiggleSortII.swift)| Medium| O(nlogn)| O(n)|
[Sort Transformed Array](https://leetcode.com/problems/sort-transformed-array/)| [Swift](./Sort/SortTransformedArray.swift)| Medium| O(n)| O(1)|
[Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/)| [Swift](./Sort/TopKFrequentElements.swift)| Medium| O(nlogn)| O(n)|
[Meeting Rooms](https://leetcode.com/problems/meeting-rooms/)| [Swift](./Sort/MeetingRooms.swift)| Easy| O(nlogn)| O(1)|
[Meeting Rooms II](https://leetcode.com/problems/meeting-rooms-ii/)| [Swift](./Sort/MeetingRoomsII.swift)| Medium| O(nlogn)| O(n)|
[Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [Swift](./Sort/MergeIntervals.swift)| Hard| O(nlogn)| O(n)|
[Alien Dictionary](https://leetcode.com/problems/alien-dictionary/)| [Swift](./Graph/AlienDictionary.swift)| Hard| O(nm)| O(nm)|
[Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/)| [Swift](./Sort/KthLargestElementInArray.swift)| Medium| O(nlogn)| O(n)|
[Array Partition I](https://leetcode.com/problems/array-partition-i/description/)| [Swift](./Sort/ArrayPartitionI.swift)|Easy| O(nlogn)| O(n)|
[Insert Interval](https://leetcode.com/problems/insert-interval/description/)| [Swift](./Sort/InsertInterval.swift)|Hard| O(n)| O(1)|
[Largest Number](https://leetcode.com/problems/largest-number/)| [Swift](./Sort/LargestNumber.swift)| Medium| O(nlogn)| O(1)|
## Graph
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Number of Connected Components in an Undirected Graph](https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/)| [Swift](./Graph/NumberConnectedComponentsUndirectedGraph.swift)| Medium| O(nlogn)| O(n)|
[Graph Valid Tree](https://leetcode.com/problems/graph-valid-tree/)| [Swift](./Graph/GraphValidTree.swift)| Medium| O(nlogn)| O(n)|
[Number of Islands II](https://leetcode.com/problems/number-of-islands-ii/)| [Swift](./Graph/NumberIslandsII.swift)| Hard| O(klogmn)| O(mn)|
[Course Schedule](https://leetcode.com/problems/course-schedule/)| [Swift](./Graph/CourseSchedule.swift)| Medium| O(n)| O(n)|
[Course Schedule II](https://leetcode.com/problems/course-schedule-ii/)| [Swift](./Graph/CourseScheduleII.swift)| Medium| O(n)| O(n)|
## Design
| Title | Solution | Difficulty | Time | Space |
| ----- | -------- | ---------- | ---- | ----- |
[Shuffle an Array](https://leetcode.com/problems/shuffle-an-array/)| [Swift](./Design/ShuffleAnArray.swift)| Easy| O(n)| O(1)|
[Design HashMap](https://leetcode.com/problems/design-hashmap/)| [Swift](./Design/DesignHashMap.swift)| Easy| O(n)| O(n)|
[Design Tic-Tac-Toe](https://leetcode.com/problems/design-tic-tac-toe/)| [Swift](./Design/DesignTicTacToe.swift)| Medium| O(1)| O(n)|
[Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator)| [Swift](./Design/FlattenNestedListIterator.swift)| Medium| O(n)| O(n)|
[Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector/)| [Swift](./Design/Vector2D.swift)| Medium | O(n)| O(n)|
[Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/)| [Swift](./Design/ImplementTrie.swift)| Medium | O(n)| O(n)|
[Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/)| [Swift](./Design/AddSearchWord.swift)| Medium | O(24^n)| O(n)|
[Insert Delete GetRandom O(1)](https://leetcode.com/problems/insert-delete-getrandom-o1/)| [Swift](./Design/InsertDeleteGetRandom.swift)| Medium| O(1)| O(n)|
[LRU Cache](https://leetcode.com/problems/lru-cache/)| [Swift](./Design/LRUCache.swift)| Hard| O(1)| O(n)|
[All O`one Data Structure](https://leetcode.com/problems/all-oone-data-structure/)| [Swift](./Design/AllOne.swift)| Hard| O(1)| O(n)|
## Google
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Race Car](https://leetcode.com/problems/race-car/)| [Swift](./BFS/RaceCar.swift)| Hard| ★★★★★★|
[Plus One](https://leetcode.com/problems/plus-one/)| [Swift](./Math/PlusOne.swift)| Easy| ★★★★★★|
[Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Swift](./DFS/NumberofIslands.swift)| Medium| ★★★★|
[Summary Ranges](https://leetcode.com/problems/summary-ranges/)| [Swift](./Array/SummaryRanges.swift)| Medium| ★★★★|
[Perfect Squares](https://leetcode.com/problems/perfect-squares/)| [Swift](./DP/PerfectSquares.swift)| Medium| ★★★★|
[Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [Swift](./Sort/MergeIntervals.swift)| Hard| ★★★|
[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [Swift](./Stack/ValidParentheses.swift)| Easy| ★★★|
[Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)| [Swift](./Math/TrappingRainWater.swift)| Hard| ★★|
[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)| [Swift](./LinkedList/MergeKSortedLists.swift)| Hard| ★★|
[Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)| [Swift](./Array/LongestConsecutiveSequence.swift)| Hard| ★★|
[Find Peak Element](https://leetcode.com/problems/find-peak-element/)| [Swift](./Search/FindPeakElement.swift)| Medium| ★★|
[Power of Two](https://leetcode.com/problems/power-of-two/)| [Swift](./Math/PowerTwo.swift)| Easy| ★★|
[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)| [Swift](./Array/SpiralMatrix.swift)| Medium| ★★|
[Sliding Window Maximum ](https://leetcode.com/problems/sliding-window-maximum/)| [Swift](./Array/SlidingWindowMaximum.swift)| Hard| ★★|
[Pow(x, n)](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./Math/Pow.swift)| Medium| ★★|
[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| ★★|
[Heaters](https://leetcode.com/problems/heaters/)| [Swift](./Array/Heaters.swift)| Easy| ★|
## Facebook
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| ★★★★★★|
[Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)| [Swift](./String/ValidPalindrome.swift)| Easy| ★★★★★★|
[Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)| [Swift](./String/ValidPalindromeII.swift)| Easy| ★★★★★★|
[Move Zeroes](https://leetcode.com/problems/move-zeroes/)| [Swift](./Array/MoveZeroes.swift)| Easy| ★★★★★★|
[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)| [Swift](./DFS/RemoveInvalidParentheses.swift)| Hard| ★★★★★★|
[Add Binary](https://leetcode.com/problems/add-binary/)| [Swift](./Math/AddBinary.swift)| Easy| ★★★★★|
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| ★★★★★|
[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| [Swift](./Tree/BinaryTreePaths.swift)| Easy| ★★★★|
[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| ★★★★|
[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)| [Swift](./LinkedList/MergeKSortedLists.swift)| Hard| ★★★★|
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| ★★★|
[Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [Swift](./Sort/MergeIntervals.swift)| Hard| ★★★|
[Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Swift](./DFS/NumberofIslands.swift)| Medium| ★★★|
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| ★★★|
[Expression Add Operators](https://leetcode.com/problems/expression-add-operators/)| [Swift](./DFS/ExpressionAddOperators.swift)| Hard| ★★★|
[Subsets](https://leetcode.com/problems/subsets/)| [Swift](./DFS/Subsets.swift)| Medium| ★★★|
[Sort Colors](https://leetcode.com/problems/sort-colors/)| [Swift](./Sort/SortColors.swift)| Medium| ★★|
## Snapchat
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Game of Life](https://leetcode.com/problems/game-of-life/) | [Swift](./Array/GameLife.swift)| Medium| ★★★★★★|
[Meeting Rooms II](https://leetcode.com/problems/meeting-rooms-ii/)| [Swift](./Sort/MeetingRoomsII.swift)| Medium| ★★★★★★|
[Valid Sudoku](https://leetcode.com/problems/valid-sudoku/)| [Swift](./Array/ValidSudoku.swift)| Easy| ★★★★★|
[Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/)| [Swift](./Tree/BinaryTreeVerticalOrderTraversal.swift)| Medium| ★★★★|
[Alien Dictionary](https://leetcode.com/problems/alien-dictionary/)| [Swift](./Graph/AlienDictionary.swift)| Hard| ★★★★|
[One Edit Distance](https://leetcode.com/problems/one-edit-distance/)| [Swift](./String/OneEditDistance.swift)| Medium| ★★★|
[Sudoku Solver](https://leetcode.com/problems/sudoku-solver/)| [Swift](./Math/SudokuSolver.swift)| Hard| ★★★|
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| ★★|
[Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees/)| [Swift](./Tree/UniqueBinarySearchTrees.swift)| Medium| ★★|
[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)| [Swift](./String/MinimumWindowSubstring.swift)| Hard| ★★|
[Remove K Digits](https://leetcode.com/problems/remove-k-digits/)| [Swift](./Stack/RemoveKDigits.swift)| Medium| ★|
[Ternary Expression Parser](https://leetcode.com/problems/ternary-expression-parser/)| [Swift](./Stack/TernaryExpressionParser.swift)| Medium| ★|
## Uber
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Valid Sudoku](https://leetcode.com/problems/valid-sudoku/)| [Swift](./Array/ValidSudoku.swift)| Easy| ★★★★|
[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)| [Swift](./Array/SpiralMatrix.swift)| Medium| ★★★★|
[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| ★★★★|
[Group Anagrams](https://leetcode.com/problems/anagrams/)| [Swift](./String/GroupAnagrams.swift)| Medium| ★★★★|
[Word Pattern](https://leetcode.com/problems/word-pattern/)| [Swift](./String/WordPattern.swift)| Easy| ★★★|
[Roman to Integer](https://leetcode.com/problems/roman-to-integer/)| [Swift](./Math/RomanToInteger.swift)| Easy| ★★★|
[Combination Sum](https://leetcode.com/problems/combination-sum/)| [Swift](./DFS/CombinationSum.swift)| Medium| ★★|
## Airbnb
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| ★★★★★|
[Text Justification](https://leetcode.com/problems/text-justification/)| [Swift](./String/TextJustification.swift)| Hard| ★★★★|
[House Robber](https://leetcode.com/problems/house-robber/)| [Swift](./DP/HouseRobber.swift)| Easy| ★★|
[Single Number](https://leetcode.com/problems/single-number/)| [Swift](./Math/SingleNumber.swift)| Medium| ★★|
[Word Search II](https://leetcode.com/problems/word-search-ii/)| [Swift](./DFS/WordSearchII.swift)| Hard| ★★|
[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)| [Swift](./Math/AddTwoNumbers.swift)| Medium| ★★|
## LinkedIn
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Maximum Subarray](https://leetcode.com/problems/maximum-subarray/)| [Swift](./DP/MaximumSubarray.swift)| Medium| ★★★★★★|
[Pow(x, n)](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./Math/Pow.swift)| Medium| ★★★★★★|
[Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [Swift](./Sort/MergeIntervals.swift)| Hard| ★★★★★★|
[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./String/IsomorphicStrings.swift)| Easy| ★★★★★★|
[Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/)| [Swift](./Search/SearchInRotatedSortedArray.swift)| Hard| ★★★★★|
[Search for a Range](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/)| [Swift](./Search/SearchForARange.swift)| Medium| ★★★★★|
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| ★★★★|
[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/)| [Swift](./Tree/BinaryTreeLevelOrderTraversal.swift)| Easy| ★★★★|
[Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)| [Swift](./Stack/EvaluateReversePolishNotation.swift)| Medium| ★★★|
[Maximum Product Subarray](https://leetcode.com/problems/maximum-product-subarray/)| [Swift](./DP/MaximumProductSubarray.swift)| Medium| ★★★|
[Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)| [Swift](./Array/ProductExceptSelf.swift)| Medium| ★★★|
[Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)| [Swift](./Tree/SymmetricTree.swift)| Easy| ★★|
## Amazon
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| ★★★★★★|
[Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/)| [Swift](./DP/MinCostClimbingStairs.swift)| Easy| ★★★★|
[Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Swift](./DFS/NumberofIslands.swift)| Medium| ★★|
[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)| [Swift](./Math/AddTwoNumbers.swift)| Medium| ★★|
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| ★★|
[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [Swift](./Stack/ValidParentheses.swift)| Easy| ★★|
[Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)| [Swift](./DP/LongestPalindromicSubstring.swift)| Medium| ★★|
[Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)| [Swift](./Math/TrappingRainWater.swift)| Hard| ★★|
[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)| [Swift](./String/LongestSubstringWithoutRepeatingCharacters.swift)| Medium| ★★|
[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| ★★|
[Valid Anagram](https://leetcode.com/problems/valid-anagram/)| [Swift](./String/ValidAnagram.swift)| Easy| ★★|
[Rotate Image](https://leetcode.com/problems/rotate-image/)| [Swift](./Array/RotateImage.swift)| Medium| ★★|
[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [Swift](./DP/BestTimeBuySellStock.swift)| Easy| ★★|
[3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| ★★|
[Sliding Window Maximum ](https://leetcode.com/problems/sliding-window-maximum/)| [Swift](./Array/SlidingWindowMaximum.swift)| Hard| ★★|
## Microsoft
| Title | Solution | Difficulty | Frequency |
| ----- | -------- | ---------- | --------- |
[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [Swift](./LinkedList/ReverseLinkedList.swift)| Easy| ★★★★★★|
[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| ★★★★★|
[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)| [Swift](./Math/Atoi.swift)| Easy| ★★★★|
[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)| [Swift](./Math/AddTwoNumbers.swift)| Medium| ★★★★|
[Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/)| [Swift](./Math/ExcelSheetColumnNumber.swift)| Easy| ★★★★|
[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)| [Swift](./Tree/ValidateBinarySearchTree.swift)| Medium| ★★★|
[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| [Swift](./LinkedList/MergeTwoSortedLists.swift)| Easy| ★★★|
## Problem Status
| Solution | Number | Title | Difficulty |
| -------- | ------ | ----- | ---------- |
| [Swift](./LinkedList/LFUCache.swift) | 460 | [LFU Cache](https://oj.leetcode.com/problems/lfu-cache/) | Hard |
| [Swift](./Array/FindDisappearedNumbers.swift)| 448| [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/)| Easy|
| [Swift](./DFS/CombinationSumIV.swift) | 377 | [Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/) | Medium
| | 376 | [Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/) | Medium
| [Swift](./DP/GuessNumberHigherOrLowerII.swift) | 375 | [Guess Number Higher or Lower II](https://leetcode.com/problems/guess-number-higher-or-lower-ii/) | Medium
| | 374 | [Guess Number Higher or Lower](https://leetcode.com/problems/guess-number-higher-or-lower/) | Easy
| | 373 | [Find K Pairs with Smallest Sums](https://leetcode.com/problems/find-k-pairs-with-smallest-sums/) | Medium
| [Swift](./Math/SuperPow.swift) | 372 | [Super Pow](https://leetcode.com/problems/super-pow/) | Medium
| [Swift](./Math/SumTwoIntegers.swift) | 371 | [Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/) | Easy
| | 370 | [Range Addition](https://leetcode.com/problems/range-addition/) ♥ | Medium
| | 369 | [Plus One Linked List](https://leetcode.com/problems/plus-one-linked-list/) ♥ | Medium
| | 368 | [Largest Divisible Subset](https://leetcode.com/problems/largest-divisible-subset/) | Medium
| | 367 | [Valid Perfect Square](https://leetcode.com/problems/valid-perfect-square/) | Medium
| | 366 | [Find Leaves of Binary Tree](https://leetcode.com/problems/find-leaves-of-binary-tree/) ♥ | Medium
| | 365 | [Water and Jug Problem](https://leetcode.com/problems/water-and-jug-problem/) | Medium
| [Swift](./DP/NestedListWeightSumII.swift) | 364 | [Nested List Weight Sum II](https://leetcode.com/problems/nested-list-weight-sum-ii/) ♥ | Medium
| | 363 | [Max Sum of Rectangle No Larger Than K](https://leetcode.com/problems/max-sum-of-sub-matrix-no-larger-than-k/) | Hard
| | 362 | [Design Hit Counter](https://leetcode.com/problems/design-hit-counter/) ♥ | Medium
| | 361 | [Bomb Enemy](https://leetcode.com/problems/bomb-enemy/) ♥ | Medium
| [Swift](./Sort/SortTransformedArray.swift) | 360 | [Sort Transformed Array](https://leetcode.com/problems/sort-transformed-array/) ♥ | Medium
| | 359 | [Logger Rate Limiter](https://leetcode.com/problems/logger-rate-limiter/) ♥ | Easy
| | 358 | [Rearrange String k Distance Apart](https://leetcode.com/problems/rearrange-string-k-distance-apart/) ♥ | Hard
| | 357 | [Count Numbers with Unique Digits](https://leetcode.com/problems/count-numbers-with-unique-digits/) | Medium
| | 356 | [Line Reflection](https://leetcode.com/problems/line-reflection/) ♥ | Medium
| | 355 | [Design Twitter](https://leetcode.com/problems/design-twitter/) | Medium
| | 354 | [Russian Doll Envelopes](https://leetcode.com/problems/russian-doll-envelopes/) | Hard
| | 353 | [Design Snake Game](https://leetcode.com/problems/design-snake-game/) ♥ | Medium
| | 352 | [Data Stream as Disjoint Intervals](https://leetcode.com/problems/data-stream-as-disjoint-intervals/) | Hard
| | 351 | [Android Unlock Patterns](https://leetcode.com/problems/android-unlock-patterns/) ♥ | Medium
| [Swift](./Array/IntersectionTwoArraysII.swift) | 350 | [Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/) | Easy
| [Swift](./Array/IntersectionTwoArrays.swift) | 349 | [Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/) | Easy
| | 348 | [Design Tic-Tac-Toe](https://leetcode.com/problems/design-tic-tac-toe/) ♥ | Medium
| [Swift](./Sort/TopKFrequentElements.swift) | 347 | [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | Medium
| | 346 | [Moving Average from Data Stream](https://leetcode.com/problems/moving-average-from-data-stream/) ♥ | Easy
| [Swift](./String/ReverseVowelsOfAString.swift) | 345 | [Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/) | Easy
| [Swift](./String/ReverseString.swift) | 344 | [Reverse String](https://leetcode.com/problems/reverse-string/) | Easy
| [Swift](./Math/IntegerBreak.swift) | 343 | [Integer Break](https://leetcode.com/problems/integer-break/) | Medium
| | 342 | [Power of Four](https://leetcode.com/problems/power-of-four/) | Easy
| [Swift](./Design/FlattenNestedListIterator.swift) | 341 | [Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator/) | Medium
| [Swift](./String/LongestSubstringMostKDistinctCharacters.swift) | 340 | [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/) ♥ | Hard
| [Swift](./DP/NestedListWeightSum.swift) | 339 | [Nested List Weight Sum](https://leetcode.com/problems/nested-list-weight-sum/) ♥ | Easy
| [Swift](./Math/CountingBits.swift) | 338 | [Counting Bits](https://leetcode.com/problems/counting-bits/) | Medium
| [Swift](./Tree/HouseRobberIII.swift) | 337 | [House Robber III](https://leetcode.com/problems/house-robber-iii/) | Medium
| | 336 | [Palindrome Pairs](https://leetcode.com/problems/palindrome-pairs/) | Hard
| | 335 | [Self Crossing](https://leetcode.com/problems/self-crossing/) | Hard
| [Swift](./Tree/IncreasingTripletSubsequence.swift) | 334 | [Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/) | Medium
| | 333 | [Largest BST Subtree](https://leetcode.com/problems/largest-bst-subtree/) ♥ | Medium
| | 332 | [Reconstruct Itinerary](https://leetcode.com/problems/reconstruct-itinerary/) | Medium
| | 331 | [Verify Preorder Serialization of a Binary Tree](https://leetcode.com/problems/verify-preorder-serialization-of-a-binary-tree/) | Medium
| | 330 | [Patching Array](https://leetcode.com/problems/patching-array/) | Hard
| | 329 | [Longest Increasing Path in a Matrix](https://leetcode.com/problems/longest-increasing-path-in-a-matrix/) | Hard
| [Swift](./LinkedList/OddEvenLinkedList.swift) | 328 | [Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list/) | Medium
| | 327 | [Count of Range Sum](https://leetcode.com/problems/count-of-range-sum/) | Hard
| [Swift](./Math/PowerThree.swift) | 326 | [Power of Three](https://leetcode.com/problems/power-of-three/) | Easy
| [Swift](./Array/MaximumSizeSubarraySumEqualsK.swift) | 325 | [Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/) ♥ | Medium
| [Swift](./Sort/WiggleSortII.swift) | 324 | [Wiggle Sort II](https://leetcode.com/problems/wiggle-sort-ii/) | Medium
| [Swift](./Sort/NumberConnectedComponentsUndirectedGraph.swift) | 323 | [Number of Connected Components in an Undirected Graph](https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/) ♥ | Medium
| [Swift](./DP/CoinChange.swift) | 322 | [Coin Change](https://leetcode.com/problems/coin-change/) | Medium
| [Swift](./Array/CreateMaximumNumber.swift) | 321 | [Create Maximum Number](https://leetcode.com/problems/create-maximum-number/) | Hard
| [Swift](./DFS/GeneralizedAbbreviation.swift) | 320 | [Generalized Abbreviation](https://leetcode.com/problems/generalized-abbreviation/) ♥ | Medium
| | 319 | [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/) | Medium
| | 318 | [Maximum Product of Word Lengths](https://leetcode.com/problems/maximum-product-of-word-lengths/) | Medium
| [Swift](./BFS/ShortestDistanceAllBuildings.swift) | 317 | [Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/) ♥ | Hard
| | 316 | [Remove Duplicate Letters](https://leetcode.com/problems/remove-duplicate-letters/) | Hard
| | 315 | [Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/) | Hard
| [Swift](./Tree/BinaryTreeVerticalOrderTraversal.swift) | 314 | [Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/) ♥ | Medium
| [Swift](./Math/SuperUglyNumber.swift) | 313 | [Super Ugly Number](https://leetcode.com/problems/super-ugly-number/) | Medium
| [Swift](./DP/GuessNumberHigherOrLowerII.swift) | 312 | [Burst Balloons](https://leetcode.com/problems/burst-balloons/) | Hard
| [Swift](./Math/SparseMatrixMultiplication.swift) | 311 | [Sparse Matrix Multiplication](https://leetcode.com/problems/sparse-matrix-multiplication/) ♥ | Medium
| | 310 | [Minimum Height Trees](https://leetcode.com/problems/minimum-height-trees/) | Medium
| [Swift](./DP/BestTimeBuySellStockCooldown.swift) | 309 | [Best Time to Buy and Sell Stock with Cooldown](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/) | Medium
| | 308 | [Range Sum Query 2D - Mutable](https://leetcode.com/problems/range-sum-query-2d-mutable/) ♥ | Hard
| | 307 | [Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/) | Medium
| | 306 | [Additive Number](https://leetcode.com/problems/additive-number/) | Medium
| [Swift](./Graph/NumberIslandsII.swift) | 305 | [Number of Islands II](https://leetcode.com/problems/number-of-islands-ii/) ♥ | Hard
| [Swift](./Array/NumMatrix.swift) | 304 | [Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/) | Medium
| | 303 | [Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable/) | Easy
| | 302 | [Smallest Rectangle Enclosing Black Pixels](https://leetcode.com/problems/smallest-rectangle-enclosing-black-pixels/) ♥ | Hard
| [Swift](./DFS/RemoveInvalidParentheses.swift) | 301 | [Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/) | Hard
| [Swift](./DP/LongestIncreasingSubsequence.swift) | 300 | [Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/) | Medium
| | 299 | [Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/) | Easy |
| | 298 | [Binary Tree Longest Consecutive Sequence](https://leetcode.com/problems/binary-tree-longest-consecutive-sequence/) ♥ | Medium |
| | 297 | [Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) | Hard |
| [Swift](./Tree/UniqueBinarySearchTrees.swift) | 296 | [Best Meeting Point](https://leetcode.com/problems/best-meeting-point/) ♥ | Hard |
| | 295 | [Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/) | Hard |
| [Swift](./DP/FlipGameII.swift) | 294 | [Flip Game II](https://leetcode.com/problems/flip-game-ii/) ♥ | Medium |
| [Swift](./String/FlipGame.swift) | 293 | [Flip Game](https://leetcode.com/problems/flip-game/) ♥ | Easy |
| | 292 | [Nim Game](https://leetcode.com/problems/nim-game/) | Easy |
| | 291 | [Word Pattern II](https://leetcode.com/problems/word-pattern-ii/) ♥ | Hard |
| [Swift](./String/WordPattern.swift) | 290 | [Word Pattern](https://leetcode.com/problems/word-pattern/) | Easy |
| [Swift](./Array/GameLife.swift) | 289 | [Game of Life](https://leetcode.com/problems/game-of-life/) | Medium |
| | 288 | [Unique Word Abbreviation](https://leetcode.com/problems/unique-word-abbreviation/) ♥ | Easy |
| | 287 | [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/) | Hard |
| [Swift](./DFS/NumberofIslands.swift) | 286 | [Walls and Gates](https://leetcode.com/problems/walls-and-gates/) ♥ | Medium |
| | 285 | [Inorder Successor in BST](https://leetcode.com/problems/inorder-successor-in-bst/) ♥ | Medium |
| | 284 | [Peeking Iterator](https://leetcode.com/problems/peeking-iterator/) | Medium |
| [Swift](./Array/MoveZeroes.swift) | 283 | [Move Zeroes](https://leetcode.com/problems/move-zeroes/) | Easy |
| [Swift](./DFS/ExpressionAddOperators.swift) | 282 | [Expression Add Operators](https://leetcode.com/problems/expression-add-operators/) | Hard |
| | 281 | [Zigzag Iterator](https://leetcode.com/problems/zigzag-iterator/) ♥ | Medium |
| [Swift](./Sort/WiggleSort.swift) | 280 | [Wiggle Sort](https://leetcode.com/problems/wiggle-sort/) ♥ | Medium |
| [Swift](./DP/PerfectSquares.swift) | 279 | [Perfect Squares](https://leetcode.com/problems/perfect-squares/) | Medium |
| | 278 | [First Bad Version](https://leetcode.com/problems/first-bad-version/) | Easy |
| | 277 | [Find the Celebrity](https://leetcode.com/problems/find-the-celebrity/) ♥ | Medium |
| [Swift](./DP/PaintFence.swift) | 276 | [Paint Fence](https://leetcode.com/problems/paint-fence/) ♥ | Easy |
| | 275 | [H-Index II](https://leetcode.com/problems/h-index-ii/) | Medium |
| | 274 | [H-Index](https://leetcode.com/problems/h-index/) | Medium |
| [Swift](./Math/IntegerEnglishWords.swift) | 273 | [Integer to English Words](https://leetcode.com/problems/integer-to-english-words/) | Hard |
| [Swift](./Search/ClosestBinarySearchTreeValueII.swift) | 272 | [Closest Binary Search Tree Value II](https://leetcode.com/problems/closest-binary-search-tree-value-ii/) ♥ | Hard |
| | 271 | [Encode and Decode Strings](https://leetcode.com/problems/encode-and-decode-strings/) ♥ | Medium |
| [Swift](./Search/ClosestBinarySearchTreeValue.swift) | 270 | [Closest Binary Search Tree Value](https://leetcode.com/problems/closest-binary-search-tree-value/) ♥ | Easy |
| [Swift](./Graph/AlienDictionary.swift) | 269 | [Alien Dictionary](https://leetcode.com/problems/alien-dictionary/) ♥ | Hard |
| [Swift](./Math/MissingNumber.swift) | 268 | [Missing Number](https://leetcode.com/problems/missing-number/) | Easy |
| | 267 | [Palindrome Permutation II](https://leetcode.com/problems/palindrome-permutation-ii/) ♥ | Medium |
| [Swift](./String/PalindromePermutation.swift) | 266 | [Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation/) ♥ | Easy |
| [Swift](./DP/PaintHouseII.swift) | 265 | [Paint House II](https://leetcode.com/problems/paint-house-ii/) ♥ | Hard |
| [Swift](./Math/UglyNumberII.swift) | 264 | [Ugly Number II](https://leetcode.com/problems/ugly-number-ii/) | Medium |
| [Swift](./Math/UglyNumber.swift) | 263 | [Ugly Number](https://leetcode.com/problems/ugly-number/) | Easy |
| [Swift](./Sort/GraphValidTree.swift) | 261 | [Graph Valid Tree](https://leetcode.com/problems/graph-valid-tree/) ♥ | Medium |
| | 260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | Medium |
| | 259 | [3Sum Smaller](https://leetcode.com/problems/3sum-smaller/) ♥ | Medium |
| [Swift](./Math/AddDigits.swift) | 258 | [Add Digits](https://leetcode.com/problems/add-digits/) | Easy |
| [Swift](./Tree/BinaryTreePaths.swift) | 257 | [Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/) | Easy |
| [Swift](./DP/PaintHouse.swift) | 256 | [Paint House](https://leetcode.com/problems/paint-house/) ♥ | Medium |
| | 255 | [Verify Preorder Sequence in Binary Search Tree](https://leetcode.com/problems/verify-preorder-sequence-in-binary-search-tree/) ♥ | Medium |
| [Swift](./DFS/FactorCombinations.swift) | 254 | [Factor Combinations](https://leetcode.com/problems/factor-combinations/) ♥ | Medium |
| [Swift](./Sort/MeetingRoomsII.swift) | 253 | [Meeting Rooms II](https://leetcode.com/problems/meeting-rooms-ii/) ♥ | Medium |
| [Swift](./Sort/MeetingRooms.swift) | 252 | [Meeting Rooms](https://leetcode.com/problems/meeting-rooms/) ♥ | Easy |
| [Swift](./Design/Vector2D.swift) | 251 | [Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector/) ♥ | Medium |
| | 250 | [Count Univalue Subtrees](https://leetcode.com/problems/count-univalue-subtrees/) ♥ | Medium |
| | 249 | [Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/) ♥ | Easy |
| | 248 | [Strobogrammatic Number III](https://leetcode.com/problems/strobogrammatic-number-iii/) ♥ | Hard |
| [Swift](./DFS/StrobogrammaticNumberII.swift) | 247 | [Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii/) ♥ | Medium |
| [Swift](./Array/StrobogrammaticNumber.swift) | 246 | [Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) ♥ | Easy |
| [Swift](./Array/ShortestWordDistanceIII.swift) | 245 | [Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/) ♥ | Medium |
| [Swift](./String/ShortestWordDistanceII.swift) | 244 | [Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii/) ♥ | Medium |
| [Swift](./String/ShortestWordDistance.swift) | 243 | [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/) ♥ | Easy |
| [Swift](./String/ValidAnagram.swift) | 242 | [Valid Anagram](https://leetcode.com/problems/valid-anagram/) | Easy |
| [Swift](./DP/DifferentWaysAddParentheses.swift) | 241 | [Different Ways to Add Parentheses](https://leetcode.com/problems/different-ways-to-add-parentheses/) | Medium |
| [Swift](./Search/Search2DMatrixII.swift) | 240 | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | Medium |
| [Swift](./Array/SlidingWindowMaximum.swift) | 239 | [Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/) | Hard |
| [Swift](./Array/ProductExceptSelf.swift) | 238 | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/) | Medium |
| | 237 | [Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/) | Easy |
| | 236 | [Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) | Medium |
| [Swift](./Tree/LowestCommonAncestorBinarySearchTree.swift) | 235 | [Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/) | Easy |
| [Swift](./LinkedList/PalindromeLinkedList.swift) | 234 | [Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/) | Easy |
| | 233 | [Number of Digit One](https://leetcode.com/problems/number-of-digit-one/) | Hard |
| [Swift](./Queue/ImplementQueueUsingStacks.swift) | 232 | [Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/) | Easy |
| [Swift](./Math/PowerTwo.swift) | 231 | [Power of Two](https://leetcode.com/problems/power-of-two/) | Easy |
| [Swift](./Tree/KthSmallestElementBST.swift) | 230 | [Kth Smallest Element in a BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/) | Medium |
| [Swift](./Array/MajorityElementII.swift) | 229 | [Majority Element II](https://leetcode.com/problems/majority-element-ii/) | Medium |
| [Swift](./Array/SummaryRanges.swift) | 228 | [Summary Ranges](https://leetcode.com/problems/summary-ranges/) | Medium |
| | 227 | [Basic Calculator II](https://leetcode.com/problems/basic-calculator-ii/) | Medium |
| [Swift](./Tree/InvertBinaryTree.swift) | 226 | [Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/) | Easy |
| | 225 | [Implement Stack using Queues](https://leetcode.com/problems/implement-stack-using-queues/) | Easy |
| [Swift](./Stack/BasicCalculator.swift) | 224 | [Basic Calculator](https://leetcode.com/problems/basic-calculator/) | Hard |
| [Swift](./Math/RectangleArea.swift) | 223 | [Rectangle Area](https://leetcode.com/problems/rectangle-area/) | Easy |
| | 222 | [Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes/) | Medium |
| [Swift](./DP/MaximalSquare.swift) | 221 | [Maximal Square](https://leetcode.com/problems/maximal-square/) | Medium |
| | 220 | [Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii/) | Medium |
| [Swift](./Array/ContainsDuplicateII.swift) | 219 | [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/) | Easy |
| | 218 | [The Skyline Problem](https://leetcode.com/problems/the-skyline-problem/) | Hard |
| [Swift](./Array/ContainsDuplicate.swift) | 217 | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | Easy |
| [Swift](./DFS/combinationSumIII.swift) | 216 | [Combination Sum III](https://leetcode.com/problems/combination-sum-iii/) | Medium |
| [Swift](./Sort/KthLargestElementInArray.swift) | 215 | [Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/) | Medium |
| | 214 | [Shortest Palindrome](https://leetcode.com/problems/shortest-palindrome/) | Hard |
| [Swift](./DP/HouseRobberII.swift) | 213 | [House Robber II](https://leetcode.com/problems/house-robber-ii/) | Medium |
| [Swift](./DFS/WordSearchII.swift) | 212 | [Word Search II](https://leetcode.com/problems/word-search-ii/) | Hard |
| [Swift](./DFS/WordDictionary.swift) | 211 | [Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/) | Medium |
| [Swift](./Graph/CourseScheduleII.swift) | 210 | [Course Schedule II](https://leetcode.com/problems/course-schedule-ii/) | Medium |
| [Swift](./Array/MinimumSizeSubarraySum.swift) | 209 | [Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/) | Medium |
| [Swift](./Design/ImplementTrie.swift) | 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/) | Medium |
| [Swift](./Graph/CourseSchedule.swift) | 207 | [Course Schedule](https://leetcode.com/problems/course-schedule/) | Medium |
| [Swift](./LinkedList/ReverseLinkedList.swift) | 206 | [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/) | Easy |
| [Swift](./String/IsomorphicStrings.swift) | 205 | [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) | Easy |
| [Swift](./Math/CountPrimes.swift) | 204 | [Count Primes](https://leetcode.com/problems/count-primes/) | Easy |
| [Swift](./LinkedList/RemoveLinkedListElements.swift) | 203 | [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/) | Easy |
| [Swift](./Math/HappyNumber.swift) | 202 | [Happy Number](https://leetcode.com/problems/happy-number/) | Easy |
| | 201 | [Bitwise AND of Numbers Range](https://leetcode.com/problems/bitwise-and-of-numbers-range/) | Medium |
| [Swift](./DFS/NumberofIslands.swift) | 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/) | Medium |
| [Swift](./Tree/BinaryTreeRightSideView.swift) | 199 | [Binary Tree Right Side View](https://leetcode.com/problems/binary-tree-right-side-view/) | Medium |
| [Swift](./DP/HouseRobber.swift) | 198 | [House Robber](https://leetcode.com/problems/house-robber/) | Easy |
| | 191 | [Number of 1 Bits](https://oj.leetcode.com/problems/number-of-1-bits/) | Easy |
| | 190 | [Reverse Bits](https://oj.leetcode.com/problems/reverse-bits/) | Easy |
| [Swift](./Array/RotateArray.swift) | 189 | [Rotate Array](https://oj.leetcode.com/problems/rotate-array/) | Easy |
| [Swift](./DP/BestTimeBuySellStockIV.swift) | 188 | [Best Time to Buy and Sell Stock IV](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/) | Hard |
| | 187 | [Repeated DNA Sequences](https://oj.leetcode.com/problems/repeated-dna-sequences/) | Medium |
| [Swift](./String/ReverseWordsStringII.swift) | 186 | [Reverse Words in a String II](https://oj.leetcode.com/problems/reverse-words-in-a-string-ii/) ♥ | Medium |
| [Swift]((./Sort/LargestNumber.swift)) | 179 | [Largest Number](https://oj.leetcode.com/problems/largest-number/) | Medium |
| | 174 | [Dungeon Game](https://oj.leetcode.com/problems/dungeon-game/) | Hard |
| [Swift](./Stack/BinarySearchTreeIterator.swift) | 173 | [Binary Search Tree Iterator](https://oj.leetcode.com/problems/binary-search-tree-iterator/) | Medium |
| [Swift](./Math/FactorialTrailingZeroes.swift) | 172 | [Factorial Trailing Zeroes](https://oj.leetcode.com/problems/factorial-trailing-zeroes/) | Easy |
| [Swift](./Math/ExcelSheetColumnNumber.swift) | 171 | [Excel Sheet Column Number](https://oj.leetcode.com/problems/excel-sheet-column-number/) | Easy |
| [Swift](./Array/TwoSumIII.swift) | 170 | [Two Sum III - Data structure design](https://oj.leetcode.com/problems/two-sum-iii-data-structure-design/) ♥ | Easy |
| [Swift](./Array/MajorityElement.swift) | 169 | [Majority Element](https://oj.leetcode.com/problems/majority-element/) | Easy |
| | 168 | [Excel Sheet Column Title](https://oj.leetcode.com/problems/excel-sheet-column-title/) | Easy |
| [Swift](./Array/TwoSumII.swift) | 167 | [Two Sum II - Input array is sorted](https://oj.leetcode.com/problems/two-sum-ii-input-array-is-sorted/) ♥ | Medium |
| [Swift](./Math/FractionToRecurringDecimal.swift) | 166 | [Fraction to Recurring Decimal](https://oj.leetcode.com/problems/fraction-to-recurring-decimal/) | Medium |
| | 165 | [Compare Version Numbers](https://oj.leetcode.com/problems/compare-version-numbers/) | Easy |
| | 164 | [Maximum Gap](https://oj.leetcode.com/problems/maximum-gap/) | Hard |
| [Swift](./Array/MissingRanges.swift) | 163 | [Missing Ranges](https://oj.leetcode.com/problems/missing-ranges/) ♥ | Medium |
| [Swift](./Search/FindPeakElement.swift) | 162 | [Find Peak Element](https://oj.leetcode.com/problems/find-peak-element/) | Medium |
| [Swift](./String/OneEditDistance.swift) | 161 | [One Edit Distance](https://oj.leetcode.com/problems/one-edit-distance/)♥ | Medium |
| | 160 | [Intersection of Two Linked Lists](https://oj.leetcode.com/problems/intersection-of-two-linked-lists/) | Easy |
| [Swift](./String/LongestSubstringMostTwoDistinctCharacters.swift) | 159 | [Longest Substring with At Most Two Distinct Characters](https://oj.leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/) ♥ | Hard |
| | 158 | [Read N Characters Given Read4 II - Call multiple times](https://oj.leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/) ♥ | Hard |
| | 157 | [Read N Characters Given Read4](https://oj.leetcode.com/problems/read-n-characters-given-read4/) ♥ | Easy |
| [Swift](./Tree/BinaryTreeUpsideDown) | 156 | [Binary Tree Upside Down](https://oj.leetcode.com/problems/binary-tree-upside-down/) ♥ | Medium |
| [Swift](./Stack/MinStack.swift) | 155 | [Min Stack](https://oj.leetcode.com/problems/min-stack/) | Easy |
| [Swift](./Search/FindMinimumRotatedSortedArrayII.swift) | 154 | [Find Minimum in Rotated Sorted Array II](https://oj.leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii/) | Hard |
| [Swift](./Search/FindMinimumRotatedSortedArray.swift) | 153 | [Find Minimum in Rotated Sorted Array](https://oj.leetcode.com/problems/find-minimum-in-rotated-sorted-array/) | Medium |
| [Swift](./DP/MaximumProductSubarray.swift) | 152 | [Maximum Product Subarray](https://oj.leetcode.com/problems/maximum-product-subarray/) | Medium |
| [Swift](./String/ReverseWordsString.swift) | 151 | [Reverse Words in a String](https://oj.leetcode.com/problems/reverse-words-in-a-string/) | Medium |
| [Swift](./Stack/EvaluateReversePolishNotation.swift) | 150 | [Evaluate Reverse Polish Notation](https://oj.leetcode.com/problems/evaluate-reverse-polish-notation/) | Medium |
| | 149 | [Max Points on a Line](https://oj.leetcode.com/problems/max-points-on-a-line/) | Hard |
| | 148 | [Sort List](https://oj.leetcode.com/problems/sort-list/) | Medium |
| | 147 | [Insertion Sort List](https://oj.leetcode.com/problems/insertion-sort-list/) | Medium |
| [Swift](./LinkedList/LRUCache.swift) | 146 | [LRU Cache](https://oj.leetcode.com/problems/lru-cache/) | Hard |
| [Swift](./Stack/PostorderTraversal.swift) | 145 | [Binary Tree Postorder Traversal](https://oj.leetcode.com/problems/binary-tree-postorder-traversal/) | Hard |
| [Swift](./Stack/PreorderTraversal.swift) | 144 | [Binary Tree Preorder Traversal](https://oj.leetcode.com/problems/binary-tree-preorder-traversal/) | Medium |
| [Swift](./LinkedList/ReorderList.swift) | 143 | [Reorder List](https://oj.leetcode.com/problems/reorder-list/) | Medium |
| | 142 | [Linked List Cycle II](https://oj.leetcode.com/problems/linked-list-cycle-ii/) | Medium |
| | 141 | [Linked List Cycle](https://oj.leetcode.com/problems/linked-list-cycle/) | Easy |
| | 140 | [Word Break II](https://oj.leetcode.com/problems/word-break-ii/) | Hard |
| | 139 | [Word Break](https://oj.leetcode.com/problems/word-break/) | Medium |
| | 138 | [Copy List with Random Pointer](https://oj.leetcode.com/problems/copy-list-with-random-pointer/) | Hard |
| [Swift](./Math/SingleNumberII.swift) | 137 | [Single Number II](https://oj.leetcode.com/problems/single-number-ii/) | Medium |
| [Swift](./Math/SingleNumber.swift) | 136 | [Single Number](https://oj.leetcode.com/problems/single-number/) | Medium |
| | 135 | [Candy](https://oj.leetcode.com/problems/candy/) | Hard |
| [Swift](./Array/GasStation.swift) | 134 | [Gas Station](https://oj.leetcode.com/problems/gas-station/) | Medium |
| | 133 | [Clone Graph](https://oj.leetcode.com/problems/clone-graph/) | Medium |
| | 132 | [Palindrome Partitioning II](https://oj.leetcode.com/problems/palindrome-partitioning-ii/) | Hard |
| [Swift](./DFS/PalindromePartitioning.swift) | 131 | [Palindrome Partitioning](https://oj.leetcode.com/problems/palindrome-partitioning/) | Medium |
| | 130 | [Surrounded Regions](https://oj.leetcode.com/problems/surrounded-regions/) | Medium |
| | 129 | [Sum Root to Leaf Numbers](https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/) | Medium |
| [Swift](./Array/LongestConsecutiveSequence.swift) | 128 | [Longest Consecutive Sequence](https://oj.leetcode.com/problems/longest-consecutive-sequence/) | Hard |
| [Swift](./BFS/WordLadder.swift) | 127 | [Word Ladder](https://oj.leetcode.com/problems/word-ladder/) | Medium |
| | 126 | [Word Ladder II](https://oj.leetcode.com/problems/word-ladder-ii/) | Hard |
| [Swift](./String/ValidPalindrome.swift) | 125 | [Valid Palindrome](https://oj.leetcode.com/problems/valid-palindrome/) | Easy |
| [Swift](./Tree/BinaryTreeMaximumPathSum.swift) | 124 | [Binary Tree Maximum Path Sum](https://oj.leetcode.com/problems/binary-tree-maximum-path-sum/) | Hard |
| [Swift](./DP/BestTimeBuySellStockIII.swift) | 123 | [Best Time to Buy and Sell Stock III](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/) | Hard |
| [Swift](./DP/BestTimeBuySellStockII.swift) | 122 | [Best Time to Buy and Sell Stock II](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/) | Medium |
| [Swift](./DP/BestTimeBuySellStock.swift) | 121 | [Best Time to Buy and Sell Stock](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock/) | Easy |
| [Swift](./DP/Triangle.swift) | 120 | [Triangle](https://oj.leetcode.com/problems/triangle/) | Medium |
| | 119 | [Pascal's Triangle II](https://oj.leetcode.com/problems/pascals-triangle-ii/) | Easy |
| | 118 | [Pascal's Triangle](https://oj.leetcode.com/problems/pascals-triangle/) | Easy |
| | 117 | [Populating Next Right Pointers in Each Node II](https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/) | Hard |
| | 116 | [Populating Next Right Pointers in Each Node](https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node/) | Medium |
| | 115 | [Distinct Subsequences](https://oj.leetcode.com/problems/distinct-subsequences/) | Hard |
| [Swift](./Tree/FlattenBinaryTreeLinkedList.swift) | 114 | [Flatten Binary Tree to Linked List](https://oj.leetcode.com/problems/flatten-binary-tree-to-linked-list/) | Medium |
| [Swift](./Tree/PathSumII.swift) | 113 | [Path Sum II](https://oj.leetcode.com/problems/path-sum-ii/) | Medium |
| [Swift](./Tree/PathSum.swift) | 112 | [Path Sum](https://oj.leetcode.com/problems/path-sum/) | Easy |
| [Swift](./Tree/MinimumDepthOfBinaryTree.swift) | 111 | [Minimum Depth of Binary Tree](https://oj.leetcode.com/problems/minimum-depth-of-binary-tree/) | Easy |
| [Swift](./Tree/BalancedBinaryTree.swift) | 110 | [Balanced Binary Tree](https://oj.leetcode.com/problems/balanced-binary-tree/) | Easy |
| | 109 | [Convert Sorted List to Binary Search Tree](https://oj.leetcode.com/problems/convert-sorted-list-to-binary-search-tree/) | Medium |
| [Swift](./Tree/ConvertSortedArrayBinarySearchTree.swift) | 108 | [Convert Sorted Array to Binary Search Tree](https://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) | Medium |
| [Swift](./Tree/BinaryTreeLevelOrderTraversalII.swift) | 107 | [Binary Tree Level Order Traversal II](https://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/) | Easy |
| [Swift](./Tree/ConstructBinaryTreeInorderPostorder.swift) | 106 | [Construct Binary Tree from Inorder and Postorder Traversal](https://oj.leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) | Medium |
| [Swift](./Tree/ConstructBinaryTreePreorderInorder.swift) | 105 | [Construct Binary Tree from Preorder and Inorder Traversal](https://oj.leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) | Medium |
| [Swift](./Tree/MaximumDepthOfBinaryTree.swift) | 104 | [Maximum Depth of Binary Tree](https://oj.leetcode.com/problems/maximum-depth-of-binary-tree/) | Easy |
| [Swift](./Tree/BinaryTreeZigzagLevelOrderTraversal.swift) | 103 | [Binary Tree Zigzag Level Order Traversal](https://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) | Medium |
| [Swift](./Tree/BinaryTreeLevelOrderTraversal.swift) | 102 | [Binary Tree Level Order Traversal](https://oj.leetcode.com/problems/binary-tree-level-order-traversal/) | Easy |
| [Swift](./Tree/SymmetricTree.swift) | 101 | [Symmetric Tree](https://oj.leetcode.com/problems/symmetric-tree/) | Easy |
| [Swift](./Tree/SameTree.swift) | 100 | [Same Tree](https://oj.leetcode.com/problems/same-tree/) | Easy |
| [Swift](./Tree/RecoverBinarySearchTree.swift) | 99 | [Recover Binary Search Tree](https://oj.leetcode.com/problems/recover-binary-search-tree/) | Hard |
| [Swift](./Tree/ValidateBinarySearchTree.swift) | 98 | [Validate Binary Search Tree](https://oj.leetcode.com/problems/validate-binary-search-tree/) | Medium |
| | 97 | [Interleaving String](https://oj.leetcode.com/problems/interleaving-string/) | Hard |
| [Swift](./Tree/UniqueBinarySearchTrees.swift) | 96 | [Unique Binary Search Trees](https://oj.leetcode.com/problems/unique-binary-search-trees/) | Medium |
| | 95 | [Unique Binary Search Trees II](https://oj.leetcode.com/problems/unique-binary-search-trees-ii/) | Medium |
| [Swift](./Stack/InorderTraversal.swift) | 94 | [Binary Tree Inorder Traversal](https://oj.leetcode.com/problems/binary-tree-inorder-traversal/) | Medium |
| | 93 | [Restore IP Addresses](https://oj.leetcode.com/problems/restore-ip-addresses/) | Medium |
| | 92 | [Reverse Linked List II](https://oj.leetcode.com/problems/reverse-linked-list-ii/) | Medium |
| [Swift](./DP/DecodeWays.swift) | 91 | [Decode Ways](https://oj.leetcode.com/problems/decode-ways/) | Medium |
| [Swift](./DFS/SubsetsII.swift) | 90 | [Subsets II](https://oj.leetcode.com/problems/subsets-ii/) | Medium |
| [Swift](./Math/GaryCode.swift) | 89 | [Gray Code](https://oj.leetcode.com/problems/gray-code/) | Medium |
| [Swift](./Sort/MergeSortedArray.swift) | 88 | [Merge Sorted Array](https://oj.leetcode.com/problems/merge-sorted-array/) | Easy |
| | 87 | [Scramble String](https://oj.leetcode.com/problems/scramble-string/) | Hard |
| [Swift](./LinkedList/PartitionList.swift) | 86 | [Partition List](https://oj.leetcode.com/problems/partition-list/) | Medium |
| | 85 | [Maximal Rectangle](https://oj.leetcode.com/problems/maximal-rectangle/) | Hard |
| | 84 | [Largest Rectangle in Histogram](https://oj.leetcode.com/problems/largest-rectangle-in-histogram/) | Hard |
| [Swift](./LinkedList/RemoveDuplicatesFromSortedList.swift) | 83 | [Remove Duplicates from Sorted List](https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list/) | Easy |
| [Swift](./LinkedList/RemoveDuplicatesFromSortedListII.swift) | 82 | [Remove Duplicates from Sorted List II](https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list-ii/) | Medium |
| [Swift](./Search/SearchInRotatedSortedArrayII.swift) | 81 | [Search in Rotated Sorted Array II](https://oj.leetcode.com/problems/search-in-rotated-sorted-array-ii/) | Medium |
| [Swift](./Array/RemoveDuplicatesFromSortedArrayII.swift) | 80 | [Remove Duplicates from Sorted Array II](https://oj.leetcode.com/problems/remove-duplicates-from-sorted-array-ii/) | Medium |
| [Swift](./DFS/WordSearch.swift) | 79 | [Word Search](https://oj.leetcode.com/problems/word-search/) | Medium |
| [Swfit](./DFS/Subsets.swift) | 78 | [Subsets](https://oj.leetcode.com/problems/subsets/) | Medium |
| [Swift](./DFS/combinations.swift) | 77 | [Combinations](https://oj.leetcode.com/problems/combinations/) | Medium |
| [Swift](./Array/MinimumWindowSubstring.swift) | 76 | [Minimum Window Substring](https://oj.leetcode.com/problems/minimum-window-substring/) | Hard |
| [Swift](./Sort/SortColors.swift) | 75 | [Sort Colors](https://oj.leetcode.com/problems/sort-colors/) | Medium |
| [Swift](./Search/Search2DMatrix.swift) | 74 | [Search a 2D Matrix](https://oj.leetcode.com/problems/search-a-2d-matrix/) | Medium |
| [Swift](./Array/SetMatrixZero.swift) | 73 | [Set Matrix Zeroes](https://oj.leetcode.com/problems/set-matrix-zeroes/) | Medium |
| [Swift](./DP/EditDistance.swift) | 72 | [Edit Distance](https://oj.leetcode.com/problems/edit-distance/) | Hard |
| [Swift](./Stack/SimplifyPath.swift) | 71 | [Simplify Path](https://oj.leetcode.com/problems/simplify-path/) | Medium |
| [Swift](./DP/ClimbingStairs.swift) | 70 | [Climbing Stairs](https://oj.leetcode.com/problems/climbing-stairs/) | Easy |
| [Swift](./Search/Sqrtx.swift) | 69 | [Sqrt(x)](https://oj.leetcode.com/problems/sqrtx/) | Medium |
| [Swift](./String/TextJustification.swift) | 68 | [Text Justification](https://oj.leetcode.com/problems/text-justification/) | Hard |
| [Swift](./Math/AddBinary.swift) | 67 | [Add Binary](https://oj.leetcode.com/problems/add-binary/) | Easy |
| [Swift](./Math/PlusOne.swift) | 66 | [Plus One](https://oj.leetcode.com/problems/plus-one/) | Easy |
| [Swift](./Math/ValidNumber.swift) | 65 | [Valid Number](https://oj.leetcode.com/problems/valid-number/) | Hard |
| [Swift](./DP/MinimumPathSum.swift) | 64 | [Minimum Path Sum](https://oj.leetcode.com/problems/minimum-path-sum/) | Medium |
| [Swift](./DP/UniquePathsII.swift) | 63 | [Unique Paths II](https://oj.leetcode.com/problems/unique-paths-ii/) | Medium |
| [Swift](./DP/UniquePaths.swift) | 62 | [Unique Paths](https://oj.leetcode.com/problems/unique-paths/) | Medium |
| [Swift](./LinkedList/RotateList.swift) | 61 | [Rotate List](https://oj.leetcode.com/problems/rotate-list/) | Medium |
| [Swift](./Math/PermutationSequence.swift) | 60 | [Permutation Sequence](https://oj.leetcode.com/problems/permutation-sequence/) | Medium |
| [Swift](./Array/SpiralMatrixII.swift) | 59 | [Spiral Matrix II](https://oj.leetcode.com/problems/spiral-matrix-ii/) | Medium |
| [Swift](./String/LengthLastWord.swift) | 58 | [Length of Last Word](https://oj.leetcode.com/problems/length-of-last-word/) | Easy |
| [Swift](./Sort/InsertInterval.swift) | 57 | [Insert Interval](https://oj.leetcode.com/problems/insert-interval/) | Hard |
| [Swift](./Sort/MergeIntervals.swift) | 56 | [Merge Intervals](https://oj.leetcode.com/problems/merge-intervals/) | Hard |
| [Swift](./DP/JumpGame.swift) | 55 | [Jump Game](https://oj.leetcode.com/problems/jump-game/) | Medium |
| [Swift](./Array/SpiralMatrix.swift) | 54 | [Spiral Matrix](https://oj.leetcode.com/problems/spiral-matrix/) | Medium |
| [Swift](./DP/MaximumSubarray.swift) | 53 | [Maximum Subarray](https://oj.leetcode.com/problems/maximum-subarray/) | Medium |
| [Swift](./DFS/NQueensII.swift) | 52 | [N-Queens II](https://oj.leetcode.com/problems/n-queens-ii/) | Hard |
| [Swift](./DFS/NQueens.swift) | 51 | [N-Queens](https://oj.leetcode.com/problems/n-queens/) | Hard |
| [Swift](./Math/Pow.swift) | 50 | ["Pow(x, n)"](https://oj.leetcode.com/problems/powx-n/) | Medium |
| [Swift](./String/GroupAnagrams.swift) | 49 | [Group Anagrams](https://oj.leetcode.com/problems/anagrams/) | Medium |
| [Swift](./Array/RotateImage.swift) | 48 | [Rotate Image](https://oj.leetcode.com/problems/rotate-image/) | Medium |
| [Swift](./DFS/PermutationsII.swift) | 47 | [Permutations II](https://oj.leetcode.com/problems/permutations-ii/) | Medium |
| [Swift](./DFS/Permutations.swift) | 46 | [Permutations](https://oj.leetcode.com/problems/permutations/) | Medium |
| | 45 | [Jump Game II](https://oj.leetcode.com/problems/jump-game-ii/) | Hard |
| [Swift](./DP/WildcardMatching.swift) | 44 | [Wildcard Matching](https://oj.leetcode.com/problems/wildcard-matching/) | Hard |
| [Swift](./String/MultiplyStrings.swift) | 43 | [Multiply Strings](https://oj.leetcode.com/problems/multiply-strings/) | Medium |
| [Swift](./Math/TrappingRainWater.swift) | 42 | [Trapping Rain Water](https://oj.leetcode.com/problems/trapping-rain-water/) | Hard |
| [Swift](./Array/FirstMissingPositive.swift) | 41 | [First Missing Positive](https://oj.leetcode.com/problems/first-missing-positive/) | Hard |
| [Swift](./DFS/combinationSumII.swiftc) | 40 | [Combination Sum II](https://oj.leetcode.com/problems/combination-sum-ii/) | Medium |
| [Swift](./DFS/CombinationSum.swift) | 39 | [Combination Sum](https://oj.leetcode.com/problems/combination-sum/) | Medium |
| [Swift](./String/CountAndSay.swift) | 38 | [Count and Say](https://oj.leetcode.com/problems/count-and-say/) | Easy |
| [Swift](./Math/SudokuSolver.swift) | 37 | [Sudoku Solver](https://oj.leetcode.com/problems/sudoku-solver/) | Hard |
| [Swift](./Array/ValidSudoku.swift) | 36 | [Valid Sudoku](https://oj.leetcode.com/problems/valid-sudoku/) | Easy |
| [Swift](./Search/SearchInsertPosition.swift) | 35 | [Search Insert Position](https://oj.leetcode.com/problems/search-insert-position/) | Medium |
| [Swift](./Search/SearchForARange.swift) | 34 | [Search for a Range](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) | Medium |
| [Swift](./Search/SearchInRotatedSortedArray.swift) | 33 | [Search in Rotated Sorted Array](https://oj.leetcode.com/problems/search-in-rotated-sorted-array/) | Hard |
| [Swift](./Stack/LongestValidParentheses.swift) | 32 | [Longest Valid Parentheses](https://oj.leetcode.com/problems/longest-valid-parentheses/) | Hard |
| [Swift](./Array/NextPermutation.swift) | 31 | [Next Permutation](https://oj.leetcode.com/problems/next-permutation/) | Medium |
| | 30 | [Substring with Concatenation of All Words](https://oj.leetcode.com/problems/substring-with-concatenation-of-all-words/) | Hard |
| [Swift](./Math/DivideTwoIntegers.swift) | 29 | [Divide Two Integers](https://oj.leetcode.com/problems/divide-two-integers/) | Medium |
| [Swift](./String/StrStr.swift) | 28 | [Implement strStr()](https://oj.leetcode.com/problems/implement-strstr/) | Easy |
| [Swfit](./Array/RemoveElement.swift) | 27 | [Remove Element](https://oj.leetcode.com/problems/remove-element/) | Easy |
| [Swift](./Array/RemoveDuplicatesFromSortedArray.swift) | 26 | [Remove Duplicates from Sorted Array](https://oj.leetcode.com/problems/remove-duplicates-from-sorted-array/) | Easy |
| [Swift](./LinkedList/ReverseNodesInKGroup.swift) | 25 | [Reverse Nodes in k-Group](https://oj.leetcode.com/problems/reverse-nodes-in-k-group/) | Hard |
| [Swift](./LinkedList/SwapNodesInPairs.swift) | 24 | [Swap Nodes in Pairs](https://oj.leetcode.com/problems/swap-nodes-in-pairs/) | Easy |
| [Swift](./LinkedList/MergeKSortedLists.swift) | 23 | [Merge k Sorted Lists](https://oj.leetcode.com/problems/merge-k-sorted-lists/) | Hard |
| [Swift](./Math/GenerateParentheses.swift) | 22 | [Generate Parentheses](https://oj.leetcode.com/problems/generate-parentheses/) | Medium |
| [Swift](./LinkedList/MergeTwoSortedLists.swift) | 21 | [Merge Two Sorted Lists](https://oj.leetcode.com/problems/merge-two-sorted-lists/) | Easy |
| [Swift](./Stack/ValidParentheses.swift) | 20 | [Valid Parentheses](https://oj.leetcode.com/problems/valid-parentheses/) | Easy |
| [Swift](./LinkedList/RemoveNthFromEnd.swift) | 19 | [Remove Nth Node From End of List](https://oj.leetcode.com/problems/remove-nth-node-from-end-of-list/) | Easy |
| [Swift](./Array/FourSum.swift) | 18 | [4Sum](https://oj.leetcode.com/problems/4sum/) | Medium |
| [Swift](./DFS/LetterCombinationsPhoneNumber.swift) | 17 | [Letter Combinations of a Phone Number](https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/) | Medium |
| [Swift](./Array/ThreeSum.swift) | 16 | [3Sum Closest](https://oj.leetcode.com/problems/3sum-closest/) | Medium |
| [Swift](./Array/ThreeSum.swift) | 15 | [3Sum](https://oj.leetcode.com/problems/3sum/) | Medium |
| [Swift](./String/LongestCommonPrefix.swift) | 14 | [Longest Common Prefix](https://oj.leetcode.com/problems/longest-common-prefix/) | Easy |
| [Swift](./Math/RomanToInteger.swift) | 13 | [Roman to Integer](https://oj.leetcode.com/problems/roman-to-integer/) | Easy |
| [Swift](./Math/IntegerToRoman.swift) | 12 | [Integer to Roman](https://oj.leetcode.com/problems/integer-to-roman/) | Medium |
| [Swift](./Math/ContainerMostWater.swift) | 11 | [Container With Most Water](https://oj.leetcode.com/problems/container-with-most-water/) | Medium |
| [Swift](./DP/RegularExpressionMatching.swift) | 10 | [Regular Expression Matching](https://oj.leetcode.com/problems/regular-expression-matching/) | Hard |
| [Swift](./Math/PalindromeNumber.swift) | 9 | [Palindrome Number](https://oj.leetcode.com/problems/palindrome-number/) | Easy |
| [Swift](./Math/Atoi.swift) | 8 | [String to Integer (atoi)](https://oj.leetcode.com/problems/string-to-integer-atoi/) | Easy |
| [Swift](./Math/ReverseInteger.swift) | 7 | [Reverse Integer](https://oj.leetcode.com/problems/reverse-integer/) | Easy |
| [Swift](./String/ZigZagConversion.swift) | 6 | [ZigZag Conversion](https://oj.leetcode.com/problems/zigzag-conversion/) | Easy |
| [Swift](./DP/LongestPalindromicSubstring.swift) | 5 | [Longest Palindromic Substring](https://oj.leetcode.com/problems/longest-palindromic-substring/) | Medium |
| [Swift](./Search/MedianOfTwoSortedArrays.swift) | 4 | [Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/) | Hard |
| [Swift](./String/LongestSubstringWithoutRepeatingCharacters.swift) | 3 | [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | Medium |
| [Swift](./Math/AddTwoNumbers.swift) | 2 | [Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | Medium |
| [Swift](./Array/TwoSum.swift) | 1 | [Two Sum](https://leetcode.com/problems/two-sum/) | Easy |