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https://github.com/kulikov-dev/leetcodenet

LeetCode problems with detailed explanation and different solutions.
https://github.com/kulikov-dev/leetcodenet

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LeetCode problems with detailed explanation and different solutions.

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## LeetCodeNet

LeetCode problems with clean code, detailed explanations and different easy-understandable solutions.

All problems are grouped by patterns, so you can train in solving of specific type of problems.



### Level: Easy



#### Pattern: without

* #9: Palindrome Number (Math)

* #13: Roman to Integer (Math)

* #20: Valid Parentheses (String)

* #21: Merge Two Sorted Lists (Linked List)

* #66: Plus One (Array)

* #118: Pascal's Triangle (DP)

* #155: Min Stack (DP)

* #202: Happy Number (Math)

* #206: Reverse Linked List (Linked list)

* #225: Implement Stack using Queues (Design)

* #232: Implement Queue using Stacks (Design)

* #237: Delete Node in a Linked List (Linked list)

* #303: Range Sum Query - Immutable (Design)

* #412: FizzBuzz (Math, Design)

* #414: Third Maximum Number (Array)

* #485: Max Consecutive Ones (Array)

* #566: Reshape the Matrix (Array)

* #844: Backspace String Compare (Array, Stack)

* #867: Transpose Matrix (Array)

* #976: Largest Perimeter Triangle (Math)

* #1232: Check If It Is a Straight Line (Math)

* #1281: Subtract the Product and Sum of Digits of an Integer (Math)

* #1295: Find Numbers with Even Number of Digits (Math, Array)

* #1299: Replace Elements with Greatest Element on Right Side (Array)

* #1431: Kids With the Greatest Number of Candies (Array)

* #1502: Can Make Arithmetic Progression From Sequence (Math, Array)

* #1523: Count Odd Numbers in an Interval Range (Array)

* #1539^ Kth missing positive number (Array)

* #1572: Matrix Diagonal Sum (Array)

* #1588: Sum of All Odd Length Subarrays (Array)

* #1603: Design Parking System (Design)

* #1672: Richest Customer Wealth (Array)

* #1678: Goal Parser Interpretation (String)

* #1732: Find the Highest Altitude (Array)

* #1768: Merge Strings Alternately (String)

* #1822: Sign of the Product of an Array (Math)

* #1974: Minimum Time to Type Word Using Special Typewriter (String)

* #2643: Row With Maximum Ones (Array)

* #2660: Determine the Winner of a Bowling Game (Array)

* #2716: Minimize String Length (String)

* #2733: Neither Minimum nor Maximum (Array)

* #2739: Total Distance Traveled (Math)

#### Pattern: Sorting

* #14: Longest Common Prefix (String)

* #217: Contains Duplicate (Array)

* #448: Find All Numbers Disappeared in an Array (Array)

* #1046: Last Stone Weight (Array, PriorityQueue)

* #1051: Height Checker (Array, Bucket)

* #1491: Average Salary Excluding the Minimum and Maximum Salary (Array)

#### Pattern: Prefix sum

* #724: Find Pivot Index (Array)

* #1480: Running Sum of 1d Array (Array)

* #2670: Find the Distinct Difference Array (Array)

#### Pattern: Breadth-First search (BFS)

* #104: Maximum Depth of Binary Tree (Tree)

* #112: Path Sum (Tree)

* #144: Binary Tree Preorder Traversal (Tree)

* #145: Binary Tree Postorder Traversal (Tree)

* #226: Invert Binary Tree (Tree)

* #404: Sum of Left Leaves (Tree)

* #617: Merge Two Binary Trees (Tree)

* #637: Average of Levels in Binary Tree (Tree)

* #733: Flood Fill (Array)

#### Pattern: Depth-First search (DFS)

* #94: Binary Tree Inorder Traversal (Tree)

* #101: Symmetric Tree (Tree)

* #589: N-ary Tree Preorder Traversal (Tree)

#### Pattern: Binary tree

* #235:  Lowest Common Ancestor of a Binary Search Tree (Tree)

* #700: Search in a Binary Search Tree (Tree)

#### Pattern: Two pointers

* #26: Remove Duplicates from Sorted Array (Array)

* #27: Remove Element (Array)

* #83: Remove Duplicates from Sorted List (Linked List)

* #125: Valid Palindrome (String)

* #169: Majority Element (Array)

* #203: Remove Linked List Elements (Linked List)

* #283: Move Zeroes (Array)

* #344: Reverse String (String)

* #345: Reverse Vowels of a String (String)

* #387: First Unique Character in a String (String)

* #350: Intersection of Two Arrays II (Array)

* #392: Is Subsequence (String)

* #557: Reverse Words in a String III (String)

* #696: Count Binary Substrings (String)

* #905: Sort Array By Parity (Array)

* #941: Valid Mountain Array (Array)

* #977: Squares of a Sorted Array (Array)

* #1089: Duplicate Zeroes (Array)

* #1790: Check if One String Swap Can Make Strings Equal (String)

* #2697: Lexicographically Smallest Palindrome (String)

* #2717: Semi-Ordered Permutation (Array)

#### Pattern: Two pointers: slow/fast

* #141: Linked List Cycle (Linked List)

* #234: Palindrome Linked List (Linked List)

* #876: Middle of the LInked List (Linked List)

#### Pattern: Hash table

* #1: Two Sum (Array)

* #205: Isomorphic Strings (String)

* #242: Valid Anagram (String)

* #350: Intersection of Two Arrays II (Array)

* #383: Ransom note (String)

* #389: Find the Difference (String)

* #409: Longest Palindrome (String)

* #705: Design HashSet (Design)

* #706: Design HashMap (Design)

* #953: Verifying an Alien Dictionary (String)

* #1346: Check If N and Its Double Exist (Array)

* #1394: Find Lucky Integer in an Array (Array)

* #2049: Finding 3-Digit Even Numbers (Array)

#### Pattern: Monotonic stack

* #496: Next Greater Element I (Array)

#### Pattern: Char manipulation

* #709: To Lower Case (String)

* #1309: Decrypt String from Alphabet to Integer Mapping (String)

* #1844: Replace All Digits with Characters (String)

#### Pattern: Bit manipulation

* #136: Single number (Array)

* #190: Reverse bits (Bits)

* #191: Number of 1 Bits (Bits)

* #231: Power of Two (Bits)

* #268: Missing Number (Array)

* #461: Hamming Distance (Bits)

* #1290: Convert Binary Number in a Linked List to Integer (Linked List)

* #1342: Number of Steps to Reduce a Number to Zero (Bits)

* #1356: Sort Integers by The Number of 1 Bits (Array)

#### Pattern: KMP algorithm

* #28: Implement strStr (String)

#### Pattern: Divide and conquer

* #108: Convert Sorted Array to Binary Search Tree (Tree)

#### Pattern: Binary search

* #35: Search Insert Position (Array)

* #69: Sqrt(x) (Math)

* #278: First Bad Version (Array)

* #367: Valid Perfect Square (Math)

* #374: Guess Number Higher or Lower (Array)

* #653: Two Sum IV - Input is a BST (Tree)

* #704: Binary Search (Array)

* #744: Find Smallest Letter Greater Than Target (Array)

* #1337: The K Weakest Rows in a Matrix (Array)

* #1351: Count Negative Numbers in a Sorted Matrix (Array)

* #1385: Find the Distance Value Between Two Arrays (Array)

* #1608: Special Array With X Elements Greater Than or Equal X (Array)

#### Pattern: Dynamic programming

* #70: Climbing stairs (Bottom-up)

* #746: Min Cost Climbing Stairs (Bottom-up)

* #509: Fibonacci Number (Bottom-up)

* #605: Can Place Flowers (Bottom-up)

#### Pattern: Kadane's algorithm

* #121: Best Time to Buy and Sell Stock (DP)

#### Pattern: Greedy

* #2696: Minimum String Length After Removing Substrings (String)



### Level: Medium



#### Pattern: without

* #2: Add Two Numbers (Linked list)

* #7: Reverse Integer (Math)

* #38: Count and say (String)

* #54: Spiral Matrix (Array)

* #71: Simplify Path (String)

* #382: Linked List Random Node (Linked list, Design)

* #394: Decode String (String, Stack)

* #848: Shifting Letters (String)

* #1328: Break a Palindrome (String)

* #1472: Design Browser History (Linked List, Design)

* #1980: Find Unique Binary String (Array)

* #2348: Number of Zero-Filled Subarrays (Math, Array)

* #2671: Frequency Tracker (Design)

* #2672: Number of Adjacent Elements With the Same Color (Array)

* #2718: Sum of Matrix After Queries (Array)

* #2734: Lexicographically Smallest String After Substring Operation (String)

#### Pattern: Sorting

* #347: Top K Frequent Elements (Array)

* #692: Top K Frequent Words (Array, Bucket)

* #2300: Successful Pairs of Spells and Potions (Array)

* #2740: Find the Value of the Partition (Array)

#### Pattern: Binary search

* #33: Search in Rotated Sorted Array (Array)

* #34: Find First and Last Position of Element in Sorted Array (Array)

* #74: Search a 2D Matrix (Array)

* #153: Find Minimum in Rotated Sorted Array (Array)

* #852: Peak Index in a Mountain Array (Array)

#### Pattern: Two pointers

* #5: Longest Palindromic Substring (String)

* #88: Merge Sorted Array (Array)

* #142: Linked List Cycle II (Linked List)

* #167: Two Sum II - Input Array Is Sorted (Array)

* #633: Sum of Square Numbers (Math)

* #881: Boats to Save People (Array)

* #946: Validate Stack Sequences (Array)

* #1004: Max Consecutive Ones III (Array)

* #1855: Maximum Distance Between a Pair of Values (Array)

* #2390: Removing Stars From a String (String)

#### Pattern: Two pointers: slow/fast

* #109: Convert Sorted List to Binary Search Tree (Tree, Linked list)

#### Pattern: Hash table

* #299: Bulls and Cows (Array)

* #2661: First Completely Painted Row or Column (Array)

#### Pattern: Sliding window

* #3: Longest Substring Without Repeating Characters (String)

* #424: Longest Repeating Character Replacement (String)

* #438: Find All Anagrams in a String (String)

* #567: Permutation in String (String)

* #1456: Maximum Number of Vowels in a Substring of Given Length (String)

#### Pattern: Prefix sum

* #2439: Minimize Maximum of Array (Array)

#### Pattern: Kadane's algorithm

* #53: Maximum Subarray (Array)

#### Pattern: Backtracking

* #46: Permutations (Array)

* #211: Design Add and Search Words Data Structure (Prefix Tree, Design)

* #784: Letter Case Permutation (String)

* #2698: Find the Punishment Number of an Integer (Math)

#### Pattern: Binary tree

* #98: Validate Binary Search Tree (Tree)

#### Pattern: Breadth-First search (BFS)

* #102: Binary Tree Level Order Traversal (Tree)

* #133: Clone Graph (Graph)

* #958: Check Completeness of a Binary Tree (Tree)

* #1466: Reorder Routes to Make All Paths Lead to the City Zero (Graph)

* #2583: Kth Largest Sum in a Binary Tree (Tree)

#### Pattern: Depth-First search (DFS)

* #129: Sum Root to Leaf Numbers (Tree)

* #200: Number of Islands (Array)

* #207: Course Schedule (Tree, Topological sort)

* #994: Rotting Oranges (Array)

* #1020: Number of Enclaves (Array)

#### Pattern: Bit manipulation

* #2405: Optimal Partition of String (String)

#### Pattern: Prefix Tree

* #208: Implement Trie (Design)

#### Pattern: Dynamic programming

* #62: Unique Paths (Bottom-up, Array)

* #63: Minimum Path Sum (Bottom-up, Array)

* #516: Longest Palindromic Subsequence (Bottom-up, String)

* #983: Minimum Cost For Tickets (Bottom-up, Array)

#### Pattern: Union-Find

* #1319: Number of Operations to Make Network Connected (Graph)

* #2316: Count Unreachable Pairs of Nodes in an Undirected Graph (Graph)



### Level: Hard



#### Pattern: without



* #23: Merge k Sorted Lists (Linked list)