{"id":16799752,"url":"https://github.com/bugenzhao/leetcode.playground","last_synced_at":"2025-04-11T00:31:50.198Z","repository":{"id":38364858,"uuid":"256462277","full_name":"BugenZhao/LeetCode.playground","owner":"BugenZhao","description":"📜 Bugen's LeetCode solutions in Swift Playground. 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Two Sum II - Input array is sorted *[Binary Search, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/intersection-of-two-linked-lists/) [[S]](LeetCode21Q1.playground/Pages/160.%20Intersection%20of%20Two%20Linked%20Lists.xcplaygroundpage/Contents.swift) 0160. Intersection of Two Linked Lists *[Linked List, Two Pointers, O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/missing-number/) [[S]](LeetCode21Q1.playground/Pages/268.%20Missing%20Number.xcplaygroundpage/Contents.swift) 0268. Missing Number \n- [X] 🤨 [[Q]](https://leetcode.com/problems/shortest-unsorted-continuous-subarray/) [[S]](LeetCode21Q1.playground/Pages/581.%20Shortest%20Unsorted%20Continuous%20Subarray.xcplaygroundpage/Contents.swift) 0581. Shortest Unsorted Continuous Subarray *[O(n), Stack]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/validate-stack-sequences/) [[S]](LeetCode21Q1.playground/Pages/946.%20Validate%20Stack%20Sequences.xcplaygroundpage/Contents.swift) 0946. Validate Stack Sequences *[O(n), Stack]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/broken-calculator/) [[S]](LeetCode21Q1.playground/Pages/991.%20Broken%20Calculator.xcplaygroundpage/Contents.swift) 0991. Broken Calculator *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses/) [[S]](LeetCode21Q1.playground/Pages/1249.%20Minimum%20Remove%20to%20Make%20Valid%20Parentheses.xcplaygroundpage/Contents.swift) 1249. Minimum Remove to Make Valid Parentheses *[O(n), Stack, String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/arithmetic-slices/) [[S]](LeetCode21Q1.playground/Pages/413.%20Arithmetic%20Slices.xcplaygroundpage/Contents.swift) 0413. Arithmetic Slices *[O(n), DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/) [[S]](LeetCode21Q1.playground/Pages/1337.%20The%20K%20Weakest%20Rows%20in%20a%20Matrix.xcplaygroundpage/Contents.swift) 1337. The K Weakest Rows in a Matrix *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/copy-list-with-random-pointer/) [[S]](LeetCode21Q1.playground/Pages/138.%20Copy%20List%20with%20Random%20Pointer.xcplaygroundpage/Contents.swift) 0138. Copy List with Random Pointer *[Linked List]*\n\n## Contests\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-211/) [[S]](./Contests/Weekly%20Contest%20211.playground/Pages/) Weekly Contest 211\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-210/) [[S]](./Contests/Weekly%20Contest%20210.playground/Pages/) Weekly Contest 210\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-209/) [[S]](./Contests/Weekly%20Contest%20209.playground/Pages/) Weekly Contest 209\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-205/) [[S]](./Contests/Weekly%20Contest%20205.playground/Pages/) Weekly Contest 205\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-203/) [[S]](./Contests/Weekly%20Contest%20203.playground/Pages/) Weekly Contest 203\n- [X] 🔖 [[C]](https://leetcode.com/contest/weekly-contest-202/) [[S]](./Contests/Weekly%20Contest%20202.playground/Pages/) Weekly Contest 202\n- [X] 🔖 [[C]](https://leetcode.com/contest/biweekly-contest-37/) [[S]](./Contests/Biweekly%20Contest%2037.playground/Pages/) Biweekly Contest 37\n\n## Problems\n- [X] 😊 [[Q]](https://leetcode.com/problems/two-sum/) [[S]](LeetCode.playground/Pages/1-Two%20Sum.xcplaygroundpage/Contents.swift) 0001. Two Sum *[Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/add-two-numbers/) [[S]](LeetCode.playground/Pages/2-Add%20Two%20Numbers.xcplaygroundpage/Contents.swift) 0002. Add Two Numbers *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/longest-substring-without-repeating-characters/) [[S]](LeetCode.playground/Pages/3-Longest%20Substring%20Without%20Repeating%20Characters.xcplaygroundpage/Contents.swift) 0003. Longest Substring Without Repeating Characters *[Array]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/median-of-two-sorted-arrays/) [[S]](LeetCode.playground/Pages/4-Median%20of%20Two%20Sorted%20Arrays.xcplaygroundpage/Contents.swift) 0004. Median of Two Sorted Arrays *[Array, Binary Search]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/longest-palindromic-substring/) [[S]](LeetCode.playground/Pages/5-Longest%20Palindromic%20Substring.xcplaygroundpage/Contents.swift) 0005. Longest Palindromic Substring *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/zigzag-conversion/) [[S]](LeetCode.playground/Pages/6-ZigZag%20Conversion.xcplaygroundpage/Contents.swift) 0006. ZigZag Conversion *[Array]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/reverse-integer/) [[S]](LeetCode.playground/Pages/7-Reverse%20Integer.xcplaygroundpage/Contents.swift) 0007. Reverse Integer *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/string-to-integer-atoi/) [[S]](LeetCode.playground/Pages/8-String%20to%20Integer%20(atoi).xcplaygroundpage/Contents.swift) 0008. String to Integer (atoi) *[String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/palindrome-number/) [[S]](LeetCode.playground/Pages/9-Palindrome%20Number.xcplaygroundpage/Contents.swift) 0009. Palindrome Number *[Mathematics]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/regular-expression-matching/) [[S]](LeetCode.playground/Pages/10.%20Regular%20Expression%20Matching.xcplaygroundpage/Contents.swift) 0010. Regular Expression Matching *[String, DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/container-with-most-water/) [[S]](LeetCode.playground/Pages/11.%20Container%20With%20Most%20Water.xcplaygroundpage/Contents.swift) 0011. Container With Most Water *[Two Pointers, Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/integer-to-roman/) [[S]](LeetCode.playground/Pages/12.%20Integer%20to%20Roman.xcplaygroundpage/Contents.swift) 0012. Integer to Roman *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/roman-to-integer/) [[S]](LeetCode.playground/Pages/13.%20Roman%20to%20Integer.xcplaygroundpage/Contents.swift) 0013. Roman to Integer *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/longest-common-prefix/) [[S]](LeetCode.playground/Pages/14.%20Longest%20Common%20Prefix.xcplaygroundpage/Contents.swift) 0014. Longest Common Prefix *[String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/3sum/) [[S]](LeetCode.playground/Pages/15.%203Sum.xcplaygroundpage/Contents.swift) 0015. 3Sum *[Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/3sum-closest/) [[S]](LeetCode.playground/Pages/16.%203Sum%20Closest.xcplaygroundpage/Contents.swift) 0016. 3Sum Closest *[Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) [[S]](LeetCode.playground/Pages/17.%20Letter%20Combinations%20of%20a%20Phone%20Number.xcplaygroundpage/Contents.swift) 0017. Letter Combinations of a Phone Number *[Array]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) [[S]](LeetCode.playground/Pages/19.%20Remove%20Nth%20Node%20From%20End%20of%20List.xcplaygroundpage/Contents.swift) 0019. Remove Nth Node From End of List *[Linked List, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/valid-parentheses/) [[S]](LeetCode.playground/Pages/20.%20Valid%20Parentheses.xcplaygroundpage/Contents.swift) 0020. Valid Parentheses *[Stack]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/merge-two-sorted-lists/) [[S]](LeetCode.playground/Pages/21.%20Merge%20Two%20Sorted%20Lists.xcplaygroundpage/Contents.swift) 0021. Merge Two Sorted Lists *[Linked List]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/generate-parentheses/) [[S]](LeetCode.playground/Pages/22.%20Generate%20Parentheses.xcplaygroundpage/Contents.swift) 0022. Generate Parentheses *[String]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/merge-k-sorted-lists/) [[S]](LeetCode.playground/Pages/23.%20Merge%20k%20Sorted%20Lists.xcplaygroundpage/Contents.swift) 0023. Merge k Sorted Lists *[Sort, Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/swap-nodes-in-pairs/) [[S]](LeetCode.playground/Pages/24.%20Swap%20Nodes%20in%20Pairs.xcplaygroundpage/Contents.swift) 0024. Swap Nodes in Pairs *[Linked List]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/reverse-nodes-in-k-group/) [[S]](LeetCode.playground/Pages/25.%20Reverse%20Nodes%20in%20k-Group.xcplaygroundpage/Contents.swift) 0025. Reverse Nodes in k-Group *[Linked List]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) [[S]](LeetCode.playground/Pages/26.%20Remove%20Duplicates%20from%20Sorted%20Array.xcplaygroundpage/Contents.swift) 0026. Remove Duplicates from Sorted Array *[Array, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/remove-element/) [[S]](LeetCode.playground/Pages/27.%20Remove%20Element.xcplaygroundpage/Contents.swift) 0027. Remove Element *[Array, Two Pointers]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/implement-strstr/) [[S]](LeetCode.playground/Pages/28.%20Implement%20strStr().xcplaygroundpage/Contents.swift) 0028. Implement strStr() *[String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/divide-two-integers/) [[S]](LeetCode.playground/Pages/29.%20Divide%20Two%20Integers.xcplaygroundpage/Contents.swift) 0029. Divide Two Integers *[Bit Manipulation, Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/next-permutation/) [[S]](LeetCode.playground/Pages/31.%20Next%20Permutation.xcplaygroundpage/Contents.swift) 0031. Next Permutation *[Sort, O(n), Binary Search]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/longest-valid-parentheses/) [[S]](LeetCode.playground/Pages/32-Longest%20Valid%20Parentheses.xcplaygroundpage/Contents.swift) 0032. Longest Valid Parentheses *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/search-in-rotated-sorted-array/) [[S]](LeetCode.playground/Pages/33.%20Search%20in%20Rotated%20Sorted%20Array.xcplaygroundpage/Contents.swift) 0033. Search in Rotated Sorted Array *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) [[S]](LeetCode.playground/Pages/34.%20Find%20First%20and%20Last%20Position%20of%20Element%20in%20Sorted%20Array.xcplaygroundpage/Contents.swift) 0034. Find First and Last Position of Element in Sorted Array *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/search-insert-position/) [[S]](LeetCode.playground/Pages/35.%20Search%20Insert%20Position.xcplaygroundpage/Contents.swift) 0035. Search Insert Position *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/valid-sudoku/) [[S]](LeetCode.playground/Pages/36.%20Valid%20Sudoku.xcplaygroundpage/Contents.swift) 0036. Valid Sudoku *[Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/count-and-say/) [[S]](LeetCode21Q1.playground/Pages/38.%20Count%20and%20Say.xcplaygroundpage/Contents.swift) 0038. Count and Say \n- [X] 🤨 [[Q]](https://leetcode.com/problems/combination-sum/) [[S]](LeetCode.playground/Pages/39.%20Combination%20Sum.xcplaygroundpage/Contents.swift) 0039. Combination Sum *[DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/combination-sum-ii/) [[S]](LeetCode.playground/Pages/40.%20Combination%20Sum%20II.xcplaygroundpage/Contents.swift) 0040. Combination Sum II *[DFS]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/first-missing-positive/) [[S]](LeetCode.playground/Pages/41.%20First%20Missing%20Positive.xcplaygroundpage/Contents.swift) 0041. First Missing Positive *[Array]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/trapping-rain-water/) [[S]](LeetCode.playground/Pages/42-Trapping%20Rain%20Water.xcplaygroundpage/Contents.swift) 0042. Trapping Rain Water *[Stack]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/multiply-strings/) [[S]](LeetCode.playground/Pages/43.%20Multiply%20Strings.xcplaygroundpage/Contents.swift) 0043. Multiply Strings *[Mathematics]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/wildcard-matching/) [[S]](LeetCode.playground/Pages/44-Wildcard%20Matching.xcplaygroundpage/Contents.swift) 0044. Wildcard Matching *[DFS, Greedy]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/jump-game-ii/) [[S]](LeetCode.playground/Pages/45-Jump%20Game%20II.xcplaygroundpage/Contents.swift) 0045. Jump Game II *[Greedy, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/permutations/) [[S]](LeetCode21Q1.playground/Pages/46.%20Permutations.xcplaygroundpage/Contents.swift) 0046. Permutations *[Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/rotate-image/) [[S]](LeetCode.playground/Pages/48.%20Rotate%20Image.xcplaygroundpage/Contents.swift) 0048. Rotate Image *[Array, Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/powx-n/) [[S]](LeetCode.playground/Pages/50-Pow(x,%20n).xcplaygroundpage/Contents.swift) 0050. Pow(x, n) *[Mathematics]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/n-queens/) [[S]](LeetCode.playground/Pages/51.%20N-Queens.xcplaygroundpage/Contents.swift) 0051. N-Queens *[DFS, Bit Manipulation]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/n-queens-ii/) [[S]](LeetCode.playground/Pages/52.%20N-Queens%20II.xcplaygroundpage/Contents.swift) 0052. N-Queens II \n- [X] 😊 [[Q]](https://leetcode.com/problems/maximum-subarray/) [[S]](LeetCode.playground/Pages/53-Maximum%20Subarray.xcplaygroundpage/Contents.swift) 0053. Maximum Subarray *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/jump-game/) [[S]](LeetCode.playground/Pages/55-Jump%20Game.xcplaygroundpage/Contents.swift) 0055. Jump Game *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/merge-intervals/) [[S]](LeetCode.playground/Pages/56.%20Merge%20Intervals.xcplaygroundpage/Contents.swift) 0056. Merge Intervals *[Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/insert-interval/) [[S]](LeetCode.playground/Pages/57.%20Insert%20Interval.xcplaygroundpage/Contents.swift) 0057. Insert Interval *[Sort]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/length-of-last-word/) [[S]](LeetCode.playground/Pages/58.%20Length%20of%20Last%20Word.xcplaygroundpage/Contents.swift) 0058. Length of Last Word \n- [X] 😫 [[Q]](https://leetcode.com/problems/permutation-sequence/) [[S]](LeetCode.playground/Pages/60.%20Permutation%20Sequence.xcplaygroundpage/Contents.swift) 0060. Permutation Sequence *[Mathematics, String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/rotate-list/) [[S]](LeetCode.playground/Pages/61.%20Rotate%20List.xcplaygroundpage/Contents.swift) 0061. Rotate List *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/unique-paths/) [[S]](LeetCode.playground/Pages/62.%20Unique%20Paths.xcplaygroundpage/Contents.swift) 0062. Unique Paths *[Mathematics, DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/unique-paths-ii/) [[S]](LeetCode.playground/Pages/63.%20Unique%20Paths%20II.xcplaygroundpage/Contents.swift) 0063. Unique Paths II *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-path-sum/) [[S]](LeetCode.playground/Pages/64.%20Minimum%20Path%20Sum.xcplaygroundpage/Contents.swift) 0064. Minimum Path Sum *[DP]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/valid-number/) [[S]](LeetCode.playground/Pages/65.%20Valid%20Number.xcplaygroundpage/Contents.swift) 0065. Valid Number *[State Machine, String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/plus-one/) [[S]](LeetCode.playground/Pages/66.%20Plus%20One.xcplaygroundpage/Contents.swift) 0066. Plus One \n- [X] 😊 [[Q]](https://leetcode.com/problems/add-binary/) [[S]](LeetCode.playground/Pages/67.%20Add%20Binary.xcplaygroundpage/Contents.swift) 0067. Add Binary \n- [X] 😊 [[Q]](https://leetcode.com/problems/sqrtx/) [[S]](LeetCode.playground/Pages/69-Sqrt(x).xcplaygroundpage/Contents.swift) 0069. Sqrt(x) *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/climbing-stairs/) [[S]](LeetCode.playground/Pages/70-Climbing%20Stairs.xcplaygroundpage/Contents.swift) 0070. Climbing Stairs *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/simplify-path/) [[S]](LeetCode21Q1.playground/Pages/71.%20Simplify%20Path.xcplaygroundpage/Contents.swift) 0071. Simplify Path *[Stack]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/edit-distance/) [[S]](LeetCode.playground/Pages/72-Edit%20Distance.xcplaygroundpage/Contents.swift) 0072. Edit Distance *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/search-a-2d-matrix/) [[S]](LeetCode20Q4.playground/Pages/74.%20Search%20a%202D%20Matrix.xcplaygroundpage/Contents.swift) 0074. Search a 2D Matrix *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sort-colors/) [[S]](LeetCode.playground/Pages/75.%20Sort%20Colors.xcplaygroundpage/Contents.swift) 0075. Sort Colors *[Array, Two Pointers]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/minimum-window-substring/) [[S]](LeetCode.playground/Pages/76.%20Minimum%20Window%20Substring.xcplaygroundpage/Contents.swift) 0076. Minimum Window Substring *[Sliding Windows, Hash Table, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/subsets/) [[S]](LeetCode.playground/Pages/78.%20Subsets.xcplaygroundpage/Contents.swift) 0078. Subsets *[Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/) [[S]](LeetCode.playground/Pages/80.%20Remove%20Duplicates%20from%20Sorted%20Array%20II.xcplaygroundpage/Contents.swift) 0080. Remove Duplicates from Sorted Array II *[Array, Two Pointers]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/scramble-string/) [[S]](LeetCode.playground/Pages/87-Scramble%20String.xcplaygroundpage/Contents.swift) 0087. Scramble String *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/subsets-ii/) [[S]](LeetCode.playground/Pages/90.%20Subsets%20II.xcplaygroundpage/Contents.swift) 0090. Subsets II *[Array, Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/decode-ways/) [[S]](LeetCode.playground/Pages/91-Decode%20Ways.xcplaygroundpage/Contents.swift) 0091. Decode Ways *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/reverse-linked-list-ii/) [[S]](LeetCode.playground/Pages/92.%20Reverse%20Linked%20List%20II.xcplaygroundpage/Contents.swift) 0092. Reverse Linked List II *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/unique-binary-search-trees/) [[S]](LeetCode.playground/Pages/96.%20Unique%20Binary%20Search%20Trees.xcplaygroundpage/Contents.swift) 0096. Unique Binary Search Trees *[Tree]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/interleaving-string/) [[S]](LeetCode.playground/Pages/97-Interleaving%20String.xcplaygroundpage/Contents.swift) 0097. Interleaving String *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/validate-binary-search-tree/) [[S]](LeetCode20Q4.playground/Pages/98.%20Validate%20Binary%20Search%20Tree.xcplaygroundpage/Contents.swift) 0098. Validate Binary Search Tree \n- [X] 😫 [[Q]](https://leetcode.com/problems/recover-binary-search-tree/) [[S]](LeetCode20Q4.playground/Pages/99.%20Recover%20Binary%20Search%20Tree.xcplaygroundpage/Contents.swift) 0099. Recover Binary Search Tree *[O(n), DFS, Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/same-tree/) [[S]](LeetCode.playground/Pages/100.%20Same%20Tree.xcplaygroundpage/Contents.swift) 0100. Same Tree *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-level-order-traversal/) [[S]](LeetCode.playground/Pages/102.%20Binary%20Tree%20Level%20Order%20Traversal.xcplaygroundpage/Contents.swift) 0102. Binary Tree Level Order Traversal *[Tree, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) [[S]](LeetCode.playground/Pages/103.%20Binary%20Tree%20Zigzag%20Level%20Order%20Traversal.xcplaygroundpage/Contents.swift) 0103. Binary Tree Zigzag Level Order Traversal *[Tree, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) [[S]](LeetCode.playground/Pages/105.%20Construct%20Binary%20Tree%20from%20Preorder%20and%20Inorder%20Traversal.xcplaygroundpage/Contents.swift) 0105. Construct Binary Tree from Preorder and Inorder Traversal *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) [[S]](LeetCode.playground/Pages/106.%20Construct%20Binary%20Tree%20from%20Inorder%20and%20Postorder%20Traversal.xcplaygroundpage/Contents.swift) 0106. Construct Binary Tree from Inorder and Postorder Traversal *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/) [[S]](LeetCode.playground/Pages/107.%20Binary%20Tree%20Level%20Order%20Traversal%20II.xcplaygroundpage/Contents.swift) 0107. Binary Tree Level Order Traversal II *[BFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/minimum-depth-of-binary-tree/) [[S]](LeetCode20Q4.playground/Pages/111.%20Minimum%20Depth%20of%20Binary%20Tree.xcplaygroundpage/Contents.swift) 0111. Minimum Depth of Binary Tree *[Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/path-sum/) [[S]](LeetCode.playground/Pages/112.%20Path%20Sum.xcplaygroundpage/Contents.swift) 0112. Path Sum *[Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/path-sum-ii/) [[S]](LeetCode.playground/Pages/113.%20Path%20Sum%20II.xcplaygroundpage/Contents.swift) 0113. Path Sum II *[Tree, DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/pascals-triangle/) [[S]](LeetCode.playground/Pages/118.%20Pascal's%20Triangle.xcplaygroundpage/Contents.swift) 0118. Pascal's Triangle \n- [X] 😊 [[Q]](https://leetcode.com/problems/pascals-triangle-ii/) [[S]](LeetCode.playground/Pages/119.%20Pascal's%20Triangle%20II.xcplaygroundpage/Contents.swift) 0119. Pascal's Triangle II \n- [X] 🤨 [[Q]](https://leetcode.com/problems/triangle/) [[S]](LeetCode.playground/Pages/120-Triangle.xcplaygroundpage/Contents.swift) 0120. Triangle *[DP, Graph, Shortest Path]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) [[S]](LeetCode.playground/Pages/121-Best%20Time%20to%20Buy%20and%20Sell%20Stock.xcplaygroundpage/Contents.swift) 0121. Best Time to Buy and Sell Stock *[DP, State Machine]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/) [[S]](LeetCode.playground/Pages/122-Best%20Time%20to%20Buy%20and%20Sell%20Stock%20II.xcplaygroundpage/Contents.swift) 0122. Best Time to Buy and Sell Stock II *[Greedy]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/) [[S]](LeetCode.playground/Pages/123-Best%20Time%20to%20Buy%20and%20Sell%20Stock%20III.xcplaygroundpage/Contents.swift) 0123. Best Time to Buy and Sell Stock III *[DP, State Machine]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/valid-palindrome/) [[S]](LeetCode.playground/Pages/125.%20Valid%20Palindrome.xcplaygroundpage/Contents.swift) 0125. Valid Palindrome \n- [X] 😫 [[Q]](https://leetcode.com/problems/word-ladder/) [[S]](LeetCode.playground/Pages/127-Word%20Ladder.xcplaygroundpage/Contents.swift) 0127. Word Ladder *[Graph, BFS, Shortest Path]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sum-root-to-leaf-numbers/) [[S]](LeetCode.playground/Pages/129.%20Sum%20Root%20to%20Leaf%20Numbers.xcplaygroundpage/Contents.swift) 0129. Sum Root to Leaf Numbers *[Tree, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/surrounded-regions/) [[S]](LeetCode.playground/Pages/130.%20Surrounded%20Regions.xcplaygroundpage/Contents.swift) 0130. Surrounded Regions *[Graph, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/palindrome-partitioning/) [[S]](LeetCode.playground/Pages/131-Palindrome%20Partitioning.xcplaygroundpage/Contents.swift) 0131. Palindrome Partitioning *[DP]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/palindrome-partitioning-ii/) [[S]](LeetCode.playground/Pages/132-Palindrome%20Partitioning%20II.xcplaygroundpage/Contents.swift) 0132. Palindrome Partitioning II *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/clone-graph/) [[S]](LeetCode.playground/Pages/133.%20Clone%20Graph.xcplaygroundpage/Contents.swift) 0133. Clone Graph *[Graph]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/gas-station/) [[S]](LeetCode.playground/Pages/134.%20Gas%20Station.xcplaygroundpage/Contents.swift) 0134. Gas Station *[O(n)]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/candy/) [[S]](LeetCode.playground/Pages/135.%20Candy.xcplaygroundpage/Contents.swift) 0135. Candy *[Greedy, O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/single-number/) [[S]](LeetCode.playground/Pages/136.%20Single%20Number.xcplaygroundpage/Contents.swift) 0136. Single Number *[Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/single-number-ii/) [[S]](LeetCode.playground/Pages/137.%20Single%20Number%20II.xcplaygroundpage/Contents.swift) 0137. Single Number II *[Bit Manipulation, State Machine]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/copy-list-with-random-pointer/) [[S]](LeetCode21Q1.playground/Pages/138.%20Copy%20List%20with%20Random%20Pointer.xcplaygroundpage/Contents.swift) 0138. Copy List with Random Pointer *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/word-break/) [[S]](LeetCode.playground/Pages/139-Word%20Break.xcplaygroundpage/Contents.swift) 0139. Word Break *[DP]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/word-break-ii/) [[S]](LeetCode.playground/Pages/140.%20Word%20Break%20II.xcplaygroundpage/Contents.swift) 0140. Word Break II *[DP, DFS, String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/linked-list-cycle/) [[S]](LeetCode.playground/Pages/141.%20Linked%20List%20Cycle.xcplaygroundpage/Contents.swift) 0141. Linked List Cycle *[Linked List, Two Pointers]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/linked-list-cycle-ii/) [[S]](LeetCode.playground/Pages/142.%20Linked%20List%20Cycle%20II.xcplaygroundpage/Contents.swift) 0142. Linked List Cycle II *[Linked List, Two Pointers]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/reorder-list/) [[S]](LeetCode.playground/Pages/143.%20Reorder%20List.xcplaygroundpage/Contents.swift) 0143. Reorder List *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/insertion-sort-list/) [[S]](LeetCode20Q4.playground/Pages/147.%20Insertion%20Sort%20List.xcplaygroundpage/Contents.swift) 0147. Insertion Sort List *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sort-list/) [[S]](LeetCode20Q4.playground/Pages/148.%20Sort%20List.xcplaygroundpage/Contents.swift) 0148. Sort List *[Linked List, Divide \u0026 Conquer, Sort, Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/reverse-words-in-a-string/) [[S]](LeetCode.playground/Pages/151.%20Reverse%20Words%20in%20a%20String.xcplaygroundpage/Contents.swift) 0151. Reverse Words in a String \n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximum-product-subarray/) [[S]](LeetCode.playground/Pages/152.%20Maximum%20Product%20Subarray.xcplaygroundpage/Contents.swift) 0152. Maximum Product Subarray *[DP, Divide \u0026 Conquer, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/) [[S]](LeetCode.playground/Pages/153.%20Find%20Minimum%20in%20Rotated%20Sorted%20Array.xcplaygroundpage/Contents.swift) 0153. Find Minimum in Rotated Sorted Array *[Binary Search]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii/) [[S]](LeetCode.playground/Pages/154.%20Find%20Minimum%20in%20Rotated%20Sorted%20Array%20II.xcplaygroundpage/Contents.swift) 0154. Find Minimum in Rotated Sorted Array II *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/intersection-of-two-linked-lists/) [[S]](LeetCode21Q1.playground/Pages/160.%20Intersection%20of%20Two%20Linked%20Lists.xcplaygroundpage/Contents.swift) 0160. Intersection of Two Linked Lists *[Linked List, Two Pointers, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/compare-version-numbers/) [[S]](LeetCode.playground/Pages/165.%20Compare%20Version%20Numbers.xcplaygroundpage/Contents.swift) 0165. Compare Version Numbers *[String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) [[S]](LeetCode21Q1.playground/Pages/167.%20Two%20Sum%20II%20-%20Input%20array%20is%20sorted.xcplaygroundpage/Contents.swift) 0167. Two Sum II - Input array is sorted *[Binary Search, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/majority-element/) [[S]](LeetCode.playground/Pages/169-Majority%20Element.xcplaygroundpage/Contents.swift) 0169. Majority Element *[Array, O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/excel-sheet-column-number/) [[S]](LeetCode.playground/Pages/171.%20Excel%20Sheet%20Column%20Number.xcplaygroundpage/Contents.swift) 0171. Excel Sheet Column Number \n- [X] 🔞 [[Q]](https://leetcode.com/problems/dungeon-game/) [[S]](LeetCode.playground/Pages/174.%20Dungeon%20Game.xcplaygroundpage/Contents.swift) 0174. Dungeon Game *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/largest-number/) [[S]](LeetCode.playground/Pages/179.%20Largest%20Number.xcplaygroundpage/Contents.swift) 0179. Largest Number *[Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/repeated-dna-sequences/) [[S]](LeetCode20Q4.playground/Pages/187.%20Repeated%20DNA%20Sequences.xcplaygroundpage/Contents.swift) 0187. Repeated DNA Sequences *[Hash Table]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/) [[S]](LeetCode.playground/Pages/188.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock%20IV.xcplaygroundpage/Contents.swift) 0188. Best Time to Buy and Sell Stock IV *[Greedy, DP, State Machine]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/rotate-array/) [[S]](LeetCode20Q4.playground/Pages/189.%20Rotate%20Array.xcplaygroundpage/Contents.swift) 0189. Rotate Array *[Array, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/reverse-bits/) [[S]](LeetCode.playground/Pages/190.%20Reverse%20Bits.xcplaygroundpage/Contents.swift) 0190. Reverse Bits *[Bit Manipulation]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/number-of-1-bits/) [[S]](LeetCode.playground/Pages/191.%20Number%20of%201%20Bits.xcplaygroundpage/Contents.swift) 0191. Number of 1 Bits \n- [X] 🤨 [[Q]](https://leetcode.com/problems/house-robber/) [[S]](LeetCode.playground/Pages/198.%20House%20Robber.xcplaygroundpage/Contents.swift) 0198. House Robber *[DP, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-right-side-view/) [[S]](LeetCode.playground/Pages/199-Binary%20Tree%20Right%20Side%20View.xcplaygroundpage/Contents.swift) 0199. Binary Tree Right Side View *[Tree, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/bitwise-and-of-numbers-range/) [[S]](LeetCode.playground/Pages/201.%20Bitwise%20AND%20of%20Numbers%20Range.xcplaygroundpage/Contents.swift) 0201. Bitwise AND of Numbers Range *[Bit Manipulation]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/remove-linked-list-elements/) [[S]](LeetCode.playground/Pages/203.%20Remove%20Linked%20List%20Elements.xcplaygroundpage/Contents.swift) 0203. Remove Linked List Elements *[Linked List]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/count-primes/) [[S]](LeetCode.playground/Pages/204-Count%20Primes.xcplaygroundpage/Contents.swift) 0204. Count Primes *[Mathematics]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/reverse-linked-list/) [[S]](LeetCode.playground/Pages/206.%20Reverse%20Linked%20List.xcplaygroundpage/Contents.swift) 0206. Reverse Linked List *[Linked List]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/course-schedule/) [[S]](LeetCode.playground/Pages/207-Course%20Schedule.xcplaygroundpage/Contents.swift) 0207. Course Schedule *[Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/implement-trie-prefix-tree/) [[S]](LeetCode.playground/Pages/208-Implement%20Trie%20(Prefix%20Tree).xcplaygroundpage/Contents.swift) 0208. Implement Trie (Prefix Tree) *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-size-subarray-sum/) [[S]](LeetCode.playground/Pages/209.%20Minimum%20Size%20Subarray%20Sum.xcplaygroundpage/Contents.swift) 0209. Minimum Size Subarray Sum *[Sliding Windows, Array, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/course-schedule-ii/) [[S]](LeetCode.playground/Pages/210-Course%20Schedule%20II.xcplaygroundpage/Contents.swift) 0210. Course Schedule II *[Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/design-add-and-search-words-data-structure/) [[S]](LeetCode.playground/Pages/211.%20Add%20and%20Search%20Word%20-%20Data%20structure%20design.xcplaygroundpage/Contents.swift) 0211. Design Add and Search Words Data Structure *[Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/house-robber-ii/) [[S]](LeetCode.playground/Pages/213.%20House%20Robber%20II.xcplaygroundpage/Contents.swift) 0213. House Robber II *[DP, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/combination-sum-iii/) [[S]](LeetCode.playground/Pages/216.%20Combination%20Sum%20III.xcplaygroundpage/Contents.swift) 0216. Combination Sum III *[DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/contains-duplicate/) [[S]](LeetCode.playground/Pages/217.%20Contains%20Duplicate.xcplaygroundpage/Contents.swift) 0217. Contains Duplicate *[Hash Table]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/contains-duplicate-ii/) [[S]](LeetCode.playground/Pages/219.%20Contains%20Duplicate%20II.xcplaygroundpage/Contents.swift) 0219. Contains Duplicate II *[Hash Table, Sliding Windows]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/contains-duplicate-iii/) [[S]](LeetCode.playground/Pages/220.%20Contains%20Duplicate%20III.xcplaygroundpage/Contents.swift) 0220. Contains Duplicate III *[Hash Table, Sliding Windows]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/count-complete-tree-nodes/) [[S]](LeetCode.playground/Pages/222.%20Count%20Complete%20Tree%20Nodes.xcplaygroundpage/Contents.swift) 0222. Count Complete Tree Nodes *[Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/invert-binary-tree/) [[S]](LeetCode.playground/Pages/226-Invert%20Binary%20Tree.xcplaygroundpage/Contents.swift) 0226. Invert Binary Tree *[Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/summary-ranges/) [[S]](LeetCode20Q4.playground/Pages/228.%20Summary%20Ranges.xcplaygroundpage/Contents.swift) 0228. Summary Ranges \n- [X] 🔞 [[Q]](https://leetcode.com/problems/majority-element-ii/) [[S]](LeetCode.playground/Pages/229.%20Majority%20Element%20II.xcplaygroundpage/Contents.swift) 0229. Majority Element II *[Array, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/kth-smallest-element-in-a-bst/) [[S]](LeetCode.playground/Pages/230-Kth%20Smallest%20Element%20in%20a%20BST.xcplaygroundpage/Contents.swift) 0230. Kth Smallest Element in a BST *[Tree, DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/power-of-two/) [[S]](LeetCode.playground/Pages/231-Power%20of%20Two.xcplaygroundpage/Contents.swift) 0231. Power of Two *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/delete-node-in-a-linked-list/) [[S]](LeetCode.playground/Pages/237-Delete%20Node%20in%20a%20Linked%20List.xcplaygroundpage/Contents.swift) 0237. Delete Node in a Linked List *[Linked List]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/search-a-2d-matrix-ii/) [[S]](LeetCode20Q4.playground/Pages/240.%20Search%20a%202D%20Matrix%20II.xcplaygroundpage/Contents.swift) 0240. Search a 2D Matrix II *[O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/valid-anagram/) [[S]](LeetCode.playground/Pages/242-Valid%20Anagram.xcplaygroundpage/Contents.swift) 0242. Valid Anagram *[Hash Table]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/add-digits/) [[S]](LeetCode.playground/Pages/258.%20Add%20Digits.xcplaygroundpage/Contents.swift) 0258. Add Digits *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/single-number-iii/) [[S]](LeetCode.playground/Pages/260.%20Single%20Number%20III.xcplaygroundpage/Contents.swift) 0260. Single Number III *[Bit Manipulation, O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/ugly-number/) [[S]](LeetCode.playground/Pages/263.%20Ugly%20Number.xcplaygroundpage/Contents.swift) 0263. Ugly Number \n- [X] 🤨 [[Q]](https://leetcode.com/problems/ugly-number-ii/) [[S]](LeetCode.playground/Pages/264.%20Ugly%20Number%20II.xcplaygroundpage/Contents.swift) 0264. Ugly Number II *[Mathematics, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/missing-number/) [[S]](LeetCode21Q1.playground/Pages/268.%20Missing%20Number.xcplaygroundpage/Contents.swift) 0268. Missing Number \n- [X] 🤨 [[Q]](https://leetcode.com/problems/h-index/) [[S]](LeetCode.playground/Pages/274.%20H-Index.xcplaygroundpage/Contents.swift) 0274. H-Index *[Array, Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/h-index-ii/) [[S]](LeetCode.playground/Pages/275.%20H-Index%20II.xcplaygroundpage/Contents.swift) 0275. H-Index II *[Binary Search, Array]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/first-bad-version/) [[S]](LeetCode.playground/Pages/278-First%20Bad%20Version.xcplaygroundpage/Contents.swift) 0278. First Bad Version *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/perfect-squares/) [[S]](LeetCode.playground/Pages/279.%20Perfect%20Squares.xcplaygroundpage/Contents.swift) 0279. Perfect Squares *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/peeking-iterator/) [[S]](LeetCode21Q1.playground/Pages/284.%20Peeking%20Iterator.xcplaygroundpage/Contents.swift) 0284. Peeking Iterator \n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-the-duplicate-number/) [[S]](LeetCode.playground/Pages/287.%20Find%20the%20Duplicate%20Number.xcplaygroundpage/Contents.swift) 0287. Find the Duplicate Number *[Binary Search, Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/word-pattern/) [[S]](LeetCode.playground/Pages/290.%20Word%20Pattern.xcplaygroundpage/Contents.swift) 0290. Word Pattern *[Hash Table]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/find-median-from-data-stream/) [[S]](LeetCode.playground/Pages/295.%20Find%20Median%20from%20Data%20Stream.xcplaygroundpage/Contents.swift) 0295. Find Median from Data Stream *[Heap]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/bulls-and-cows/) [[S]](LeetCode.playground/Pages/299.%20Bulls%20and%20Cows.xcplaygroundpage/Contents.swift) 0299. Bulls and Cows \n- [X] 🔞 [[Q]](https://leetcode.com/problems/longest-increasing-subsequence/) [[S]](LeetCode.playground/Pages/300.%20Longest%20Increasing%20Subsequence.xcplaygroundpage/Contents.swift) 0300. Longest Increasing Subsequence *[DP, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/) [[S]](LeetCode.playground/Pages/309.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock%20with%20Cooldown.xcplaygroundpage/Contents.swift) 0309. Best Time to Buy and Sell Stock with Cooldown *[DP, State Machine, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/minimum-height-trees/) [[S]](LeetCode.playground/Pages/310-Minimum%20Height%20Trees.xcplaygroundpage/Contents.swift) 0310. Minimum Height Trees *[Tree]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/count-of-smaller-numbers-after-self/) [[S]](LeetCode.playground/Pages/315.%20Count%20of%20Smaller%20Numbers%20After%20Self.xcplaygroundpage/Contents.swift) 0315. Count of Smaller Numbers After Self *[Sort, Divide \u0026 Conquer]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-duplicate-letters/) [[S]](LeetCode20Q4.playground/Pages/316.%20Remove%20Duplicate%20Letters.xcplaygroundpage/Contents.swift) 0316. Remove Duplicate Letters *[Greedy, DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/power-of-three/) [[S]](LeetCode.playground/Pages/326.%20Power%20of%20Three.xcplaygroundpage/Contents.swift) 0326. Power of Three \n- [X] 🤨 [[Q]](https://leetcode.com/problems/odd-even-linked-list/) [[S]](LeetCode.playground/Pages/328-Odd%20Even%20Linked%20List.xcplaygroundpage/Contents.swift) 0328. Odd Even Linked List *[Linked List]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/longest-increasing-path-in-a-matrix/) [[S]](LeetCode.playground/Pages/329-Longest%20Increasing%20Path%20in%20a%20Matrix.xcplaygroundpage/Contents.swift) 0329. Longest Increasing Path in a Matrix *[Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/reconstruct-itinerary/) [[S]](LeetCode.playground/Pages/332.%20Reconstruct%20Itinerary.xcplaygroundpage/Contents.swift) 0332. Reconstruct Itinerary *[DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/counting-bits/) [[S]](LeetCode.playground/Pages/338-Counting%20Bits.xcplaygroundpage/Contents.swift) 0338. Counting Bits *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/power-of-four/) [[S]](LeetCode.playground/Pages/342.%20Power%20of%20Four.xcplaygroundpage/Contents.swift) 0342. Power of Four *[Bit Manipulation]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/reverse-string/) [[S]](LeetCode.playground/Pages/344-Reverse%20String.xcplaygroundpage/Contents.swift) 0344. Reverse String \n- [X] 🤨 [[Q]](https://leetcode.com/problems/top-k-frequent-elements/) [[S]](LeetCode.playground/Pages/347.%20Top%20K%20Frequent%20Elements.xcplaygroundpage/Contents.swift) 0347. Top K Frequent Elements \n- [X] 😊 [[Q]](https://leetcode.com/problems/intersection-of-two-arrays-ii/) [[S]](LeetCode.playground/Pages/350.%20Intersection%20of%20Two%20Arrays%20II.xcplaygroundpage/Contents.swift) 0350. Intersection of Two Arrays II *[Two Pointers]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/valid-perfect-square/) [[S]](LeetCode.playground/Pages/367-Valid%20Perfect%20Square.xcplaygroundpage/Contents.swift) 0367. Valid Perfect Square *[Mathematics, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/largest-divisible-subset/) [[S]](LeetCode.playground/Pages/368.%20Largest%20Divisible%20Subset.xcplaygroundpage/Contents.swift) 0368. Largest Divisible Subset *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/super-pow/) [[S]](LeetCode.playground/Pages/372-Super%20Pow.xcplaygroundpage/Contents.swift) 0372. Super Pow *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/combination-sum-iv/) [[S]](LeetCode.playground/Pages/377.%20Combination%20Sum%20IV.xcplaygroundpage/Contents.swift) 0377. Combination Sum IV *[DFS, DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/insert-delete-getrandom-o1/) [[S]](LeetCode.playground/Pages/380.%20Insert%20Delete%20GetRandom%20O(1).xcplaygroundpage/Contents.swift) 0380. Insert Delete GetRandom O(1) *[Hash Table]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/ransom-note/) [[S]](LeetCode.playground/Pages/383-Ransom%20Note.xcplaygroundpage/Contents.swift) 0383. Ransom Note *[Hash Table]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/first-unique-character-in-a-string/) [[S]](LeetCode.playground/Pages/387-First%20Unique%20Character%20in%20a%20String.xcplaygroundpage/Contents.swift) 0387. First Unique Character in a String *[String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/find-the-difference/) [[S]](LeetCode.playground/Pages/389.%20Find%20the%20Difference.xcplaygroundpage/Contents.swift) 0389. Find the Difference *[Bit Manipulation]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/is-subsequence/) [[S]](LeetCode.playground/Pages/392.%20Is%20Subsequence.xcplaygroundpage/Contents.swift) 0392. Is Subsequence *[DP, Greedy, Two Pointers, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/integer-replacement/) [[S]](LeetCode.playground/Pages/397.%20Integer%20Replacement.xcplaygroundpage/Contents.swift) 0397. Integer Replacement *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/evaluate-division/) [[S]](LeetCode.playground/Pages/399-Evaluate%20Division.xcplaygroundpage/Contents.swift) 0399. Evaluate Division *[Graph, Shortest Path]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-k-digits/) [[S]](LeetCode.playground/Pages/402-Remove%20K%20Digits.xcplaygroundpage/Contents.swift) 0402. Remove K Digits *[Mathematics, Stack, Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/sum-of-left-leaves/) [[S]](LeetCode.playground/Pages/404.%20Sum%20of%20Left%20Leaves.xcplaygroundpage/Contents.swift) 0404. Sum of Left Leaves *[Tree, DFS]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/queue-reconstruction-by-height/) [[S]](LeetCode.playground/Pages/406-Queue%20Reconstruction%20by%20Height.xcplaygroundpage/Contents.swift) 0406. Queue Reconstruction by Height *[Greedy, Sort]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/longest-palindrome/) [[S]](LeetCode.playground/Pages/409-Longest%20Palindrome.xcplaygroundpage/Contents.swift) 0409. Longest Palindrome \n- [X] 😫 [[Q]](https://leetcode.com/problems/split-array-largest-sum/) [[S]](LeetCode.playground/Pages/410.%20Split%20Array%20Largest%20Sum.xcplaygroundpage/Contents.swift) 0410. Split Array Largest Sum *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/fizz-buzz/) [[S]](LeetCode.playground/Pages/412.%20Fizz%20Buzz.xcplaygroundpage/Contents.swift) 0412. Fizz Buzz \n- [X] 🤨 [[Q]](https://leetcode.com/problems/arithmetic-slices/) [[S]](LeetCode21Q1.playground/Pages/413.%20Arithmetic%20Slices.xcplaygroundpage/Contents.swift) 0413. Arithmetic Slices *[O(n), DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/pacific-atlantic-water-flow/) [[S]](LeetCode.playground/Pages/417-Pacific%20Atlantic%20Water%20Flow.xcplaygroundpage/Contents.swift) 0417. Pacific Atlantic Water Flow *[DFS, Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array/) [[S]](LeetCode.playground/Pages/421.%20Maximum%20XOR%20of%20Two%20Numbers%20in%20an%20Array.xcplaygroundpage/Contents.swift) 0421. Maximum XOR of Two Numbers in an Array *[Bit Manipulation, O(n), Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list/) [[S]](LeetCode.playground/Pages/430.%20Flatten%20a%20Multilevel%20Doubly%20Linked%20List.xcplaygroundpage/Contents.swift) 0430. Flatten a Multilevel Doubly Linked List *[Tree]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/non-overlapping-intervals/) [[S]](LeetCode.playground/Pages/435.%20Non-overlapping%20Intervals.xcplaygroundpage/Contents.swift) 0435. Non-overlapping Intervals *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-right-interval/) [[S]](LeetCode.playground/Pages/436.%20Find%20Right%20Interval.xcplaygroundpage/Contents.swift) 0436. Find Right Interval *[Hash Table, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/path-sum-iii/) [[S]](LeetCode.playground/Pages/437.%20Path%20Sum%20III.xcplaygroundpage/Contents.swift) 0437. Path Sum III *[Hash Table, Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-all-anagrams-in-a-string/) [[S]](LeetCode.playground/Pages/438-Find%20All%20Anagrams%20in%20a%20String.xcplaygroundpage/Contents.swift) 0438. Find All Anagrams in a String *[Array]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/arranging-coins/) [[S]](LeetCode.playground/Pages/441.%20Arranging%20Coins.xcplaygroundpage/Contents.swift) 0441. Arranging Coins *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-all-duplicates-in-an-array/) [[S]](LeetCode.playground/Pages/442.%20Find%20All%20Duplicates%20in%20an%20Array.xcplaygroundpage/Contents.swift) 0442. Find All Duplicates in an Array *[Array, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/serialize-and-deserialize-bst/) [[S]](LeetCode20Q4.playground/Pages/449.%20Serialize%20and%20Deserialize%20BST.xcplaygroundpage/Contents.swift) 0449. Serialize and Deserialize BST *[Tree, Stack, String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/delete-node-in-a-bst/) [[S]](LeetCode.playground/Pages/450.%20Delete%20Node%20in%20a%20BST.xcplaygroundpage/Contents.swift) 0450. Delete Node in a BST *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sort-characters-by-frequency/) [[S]](LeetCode.playground/Pages/451-Sort%20Characters%20By%20Frequency.xcplaygroundpage/Contents.swift) 0451. Sort Characters By Frequency *[Hash Table, String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/) [[S]](LeetCode20Q4.playground/Pages/452.%20Minimum%20Number%20of%20Arrows%20to%20Burst%20Balloons.xcplaygroundpage/Contents.swift) 0452. Minimum Number of Arrows to Burst Balloons *[Greedy, Sort]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/assign-cookies/) [[S]](LeetCode21Q1.playground/Pages/455.%20Assign%20Cookies.xcplaygroundpage/Contents.swift) 0455. Assign Cookies *[Greedy, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/132-pattern/) [[S]](LeetCode20Q4.playground/Pages/456.%20132%20Pattern.xcplaygroundpage/Contents.swift) 0456. 132 Pattern *[Stack, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/repeated-substring-pattern/) [[S]](LeetCode.playground/Pages/459.%20Repeated%20Substring%20Pattern.xcplaygroundpage/Contents.swift) 0459. Repeated Substring Pattern *[String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/hamming-distance/) [[S]](LeetCode.playground/Pages/461.%20Hamming%20Distance.xcplaygroundpage/Contents.swift) 0461. Hamming Distance \n- [X] 😊 [[Q]](https://leetcode.com/problems/island-perimeter/) [[S]](LeetCode.playground/Pages/463.%20Island%20Perimeter.xcplaygroundpage/Contents.swift) 0463. Island Perimeter \n- [X] 🤨 [[Q]](https://leetcode.com/problems/validate-ip-address/) [[S]](LeetCode.playground/Pages/468.%20Validate%20IP%20Address.xcplaygroundpage/Contents.swift) 0468. Validate IP Address \n- [X] 🔞 [[Q]](https://leetcode.com/problems/implement-rand10-using-rand7/) [[S]](LeetCode.playground/Pages/470.%20Implement%20Rand10()%20Using%20Rand7().xcplaygroundpage/Contents.swift) 0470. Implement Rand10() Using Rand7() *[Mathematics]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/concatenated-words/) [[S]](LeetCode.playground/Pages/472-Concatenated%20Words.xcplaygroundpage/Contents.swift) 0472. Concatenated Words *[String, Tree, DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/number-complement/) [[S]](LeetCode.playground/Pages/476-Number%20Complement.xcplaygroundpage/Contents.swift) 0476. Number Complement *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/total-hamming-distance/) [[S]](LeetCode.playground/Pages/477.%20Total%20Hamming%20Distance.xcplaygroundpage/Contents.swift) 0477. Total Hamming Distance *[Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/predict-the-winner/) [[S]](LeetCode.playground/Pages/486.%20Predict%20the%20Winner.xcplaygroundpage/Contents.swift) 0486. Predict the Winner *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/construct-the-rectangle/) [[S]](LeetCode.playground/Pages/492.%20Construct%20the%20Rectangle.xcplaygroundpage/Contents.swift) 0492. Construct the Rectangle \n- [X] 😫 [[Q]](https://leetcode.com/problems/reverse-pairs/) [[S]](LeetCode.playground/Pages/493.%20Reverse%20Pairs.xcplaygroundpage/Contents.swift) 0493. Reverse Pairs *[Sort, Two Pointers, Divide \u0026 Conquer]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/teemo-attacking/) [[S]](LeetCode.playground/Pages/495.%20Teemo%20Attacking.xcplaygroundpage/Contents.swift) 0495. Teemo Attacking *[O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/random-point-in-non-overlapping-rectangles/) [[S]](LeetCode.playground/Pages/497.%20Random%20Point%20in%20Non-overlapping%20Rectangles.xcplaygroundpage/Contents.swift) 0497. Random Point in Non-overlapping Rectangles *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/relative-ranks/) [[S]](LeetCode.playground/Pages/506.%20Relative%20Ranks.xcplaygroundpage/Contents.swift) 0506. Relative Ranks \n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-largest-value-in-each-tree-row/) [[S]](LeetCode.playground/Pages/515-Find%20Largest%20Value%20in%20Each%20Tree%20Row.xcplaygroundpage/Contents.swift) 0515. Find Largest Value in Each Tree Row *[Tree, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/coin-change-2/) [[S]](LeetCode.playground/Pages/518-Coin%20Change%202.xcplaygroundpage/Contents.swift) 0518. Coin Change 2 *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/detect-capital/) [[S]](LeetCode.playground/Pages/520.%20Detect%20Capital.xcplaygroundpage/Contents.swift) 0520. Detect Capital \n- [X] 🤨 [[Q]](https://leetcode.com/problems/contiguous-array/) [[S]](LeetCode.playground/Pages/525-Contiguous%20Array.xcplaygroundpage/Contents.swift) 0525. Contiguous Array *[Array]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/random-pick-with-weight/) [[S]](LeetCode.playground/Pages/528-Random%20Pick%20with%20Weight.xcplaygroundpage/Contents.swift) 0528. Random Pick with Weight *[Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/k-diff-pairs-in-an-array/) [[S]](LeetCode.playground/Pages/532.%20K-diff%20Pairs%20in%20an%20Array.xcplaygroundpage/Contents.swift) 0532. K-diff Pairs in an Array *[Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/single-element-in-a-sorted-array/) [[S]](LeetCode.playground/Pages/540-Single%20Element%20in%20a%20Sorted%20Array.xcplaygroundpage/Contents.swift) 0540. Single Element in a Sorted Array *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/maximum-depth-of-n-ary-tree/) [[S]](LeetCode.playground/Pages/559-Maximum%20Depth%20of%20N-ary%20Tree.xcplaygroundpage/Contents.swift) 0559. Maximum Depth of N-ary Tree *[BFS, Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/permutation-in-string/) [[S]](LeetCode.playground/Pages/567-Permutation%20in%20String.xcplaygroundpage/Contents.swift) 0567. Permutation in String \n- [X] 🤨 [[Q]](https://leetcode.com/problems/shortest-unsorted-continuous-subarray/) [[S]](LeetCode21Q1.playground/Pages/581.%20Shortest%20Unsorted%20Continuous%20Subarray.xcplaygroundpage/Contents.swift) 0581. Shortest Unsorted Continuous Subarray *[O(n), Stack]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/valid-square/) [[S]](LeetCode.playground/Pages/593.%20Valid%20Square.xcplaygroundpage/Contents.swift) 0593. Valid Square \n- [X] 😊 [[Q]](https://leetcode.com/problems/longest-harmonious-subsequence/) [[S]](LeetCode21Q1.playground/Pages/594.%20Longest%20Harmonious%20Subsequence.xcplaygroundpage/Contents.swift) 0594. Longest Harmonious Subsequence *[Hash Table]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/non-negative-integers-without-consecutive-ones/) [[S]](LeetCode.playground/Pages/600.%20Non-negative%20Integers%20without%20Consecutive%20Ones.xcplaygroundpage/Contents.swift) 0600. Non-negative Integers without Consecutive Ones *[DP, Bit Manipulation]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/task-scheduler/) [[S]](LeetCode.playground/Pages/621.%20Task%20Scheduler.xcplaygroundpage/Contents.swift) 0621. Task Scheduler *[Heap, Sort, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/course-schedule-iii/) [[S]](LeetCode.playground/Pages/630.%20Course%20Schedule%20III.xcplaygroundpage/Contents.swift) 0630. Course Schedule III *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximum-width-of-binary-tree/) [[S]](LeetCode.playground/Pages/662.%20Maximum%20Width%20of%20Binary%20Tree.xcplaygroundpage/Contents.swift) 0662. Maximum Width of Binary Tree *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/trim-a-binary-search-tree/) [[S]](LeetCode21Q1.playground/Pages/669.%20Trim%20a%20Binary%20Search%20Tree.xcplaygroundpage/Contents.swift) 0669. Trim a Binary Search Tree *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/redundant-connection/) [[S]](LeetCode21Q1.playground/Pages/684.%20Redundant%20Connection.xcplaygroundpage/Contents.swift) 0684. Redundant Connection *[Graph, Union Find]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/repeated-string-match/) [[S]](LeetCode.playground/Pages/686.%20Repeated%20String%20Match.xcplaygroundpage/Contents.swift) 0686. Repeated String Match *[String]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/binary-number-with-alternating-bits/) [[S]](LeetCode.playground/Pages/693.%20Binary%20Number%20with%20Alternating%20Bits.xcplaygroundpage/Contents.swift) 0693. Binary Number with Alternating Bits *[Bit Manipulation]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/search-in-a-binary-search-tree/) [[S]](LeetCode.playground/Pages/700.%20Search%20in%20a%20Binary%20Search%20Tree.xcplaygroundpage/Contents.swift) 0700. Search in a Binary Search Tree *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/insert-into-a-binary-search-tree/) [[S]](LeetCode.playground/Pages/701.%20Insert%20into%20a%20Binary%20Search%20Tree.xcplaygroundpage/Contents.swift) 0701. Insert into a Binary Search Tree *[Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/binary-search/) [[S]](LeetCode20Q4.playground/Pages/704.%20Binary%20Search.xcplaygroundpage/Contents.swift) 0704. Binary Search *[Binary Search, Array]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/design-hashset/) [[S]](LeetCode.playground/Pages/705.%20Design%20HashSet.xcplaygroundpage/Contents.swift) 0705. Design HashSet *[Hash Table]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/random-pick-with-blacklist/) [[S]](LeetCode.playground/Pages/710.%20Random%20Pick%20with%20Blacklist.xcplaygroundpage/Contents.swift) 0710. Random Pick with Blacklist *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/subarray-product-less-than-k/) [[S]](LeetCode.playground/Pages/713.%20Subarray%20Product%20Less%20Than%20K.xcplaygroundpage/Contents.swift) 0713. Subarray Product Less Than K *[O(n), Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/) [[S]](LeetCode.playground/Pages/714.%20Best%20Time%20to%20Buy%20and%20Sell%20Stock%20with%20Transaction%20Fee.xcplaygroundpage/Contents.swift) 0714. Best Time to Buy and Sell Stock with Transaction Fee *[DP, State Machine, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximum-length-of-repeated-subarray/) [[S]](LeetCode21Q1.playground/Pages/718.%20Maximum%20Length%20of%20Repeated%20Subarray.xcplaygroundpage/Contents.swift) 0718. Maximum Length of Repeated Subarray *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/split-linked-list-in-parts/) [[S]](LeetCode.playground/Pages/725.%20Split%20Linked%20List%20in%20Parts.xcplaygroundpage/Contents.swift) 0725. Split Linked List in Parts *[Linked List]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/flood-fill/) [[S]](LeetCode.playground/Pages/733-Flood%20Fill.xcplaygroundpage/Contents.swift) 0733. Flood Fill *[Graph, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/asteroid-collision/) [[S]](LeetCode20Q4.playground/Pages/735.%20Asteroid%20Collision.xcplaygroundpage/Contents.swift) 0735. Asteroid Collision *[Stack, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/network-delay-time/) [[S]](LeetCode.playground/Pages/743-Network%20Delay%20Time.xcplaygroundpage/Contents.swift) 0743. Network Delay Time *[Graph, Shortest Path]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/min-cost-climbing-stairs/) [[S]](LeetCode.playground/Pages/746-Min%20Cost%20Climbing%20Stairs.xcplaygroundpage/Contents.swift) 0746. Min Cost Climbing Stairs *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/partition-labels/) [[S]](LeetCode.playground/Pages/763.%20Partition%20Labels.xcplaygroundpage/Contents.swift) 0763. Partition Labels *[Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/jewels-and-stones/) [[S]](LeetCode.playground/Pages/771-Jewels%20and%20Stones%20.xcplaygroundpage/Contents.swift) 0771. Jewels and Stones *[Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/letter-case-permutation/) [[S]](LeetCode.playground/Pages/784.%20Letter%20Case%20Permutation.xcplaygroundpage/Contents.swift) 0784. Letter Case Permutation \n- [X] 🤨 [[Q]](https://leetcode.com/problems/is-graph-bipartite/) [[S]](LeetCode.playground/Pages/785.%20Is%20Graph%20Bipartite?.xcplaygroundpage/Contents.swift) 0785. Is Graph Bipartite? *[Graph, DFS]*\n- [X] 📝 [[Q]](https://leetcode.com/problems/cheapest-flights-within-k-stops/) [[S]](LeetCode.playground/Pages/787.%20Cheapest%20Flights%20Within%20K%20Stops.xcplaygroundpage/Contents.swift) 0787. Cheapest Flights Within K Stops *[Graph, Shortest Path]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/all-paths-from-source-to-target/) [[S]](LeetCode.playground/Pages/797.%20All%20Paths%20From%20Source%20to%20Target.xcplaygroundpage/Contents.swift) 0797. All Paths From Source to Target *[DFS, Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/champagne-tower/) [[S]](LeetCode20Q4.playground/Pages/799.%20Champagne%20Tower.xcplaygroundpage/Contents.swift) 0799. Champagne Tower *[DP]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/bus-routes/) [[S]](LeetCode.playground/Pages/815.%20Bus%20Routes.xcplaygroundpage/Contents.swift) 0815. Bus Routes *[BFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/shortest-distance-to-a-character/) [[S]](LeetCode21Q1.playground/Pages/821.%20Shortest%20Distance%20to%20a%20Character.xcplaygroundpage/Contents.swift) 0821. Shortest Distance to a Character *[O(n)]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/goat-latin/) [[S]](LeetCode.playground/Pages/824.%20Goat%20Latin.xcplaygroundpage/Contents.swift) 0824. Goat Latin \n- [X] 😊 [[Q]](https://leetcode.com/problems/flipping-an-image/) [[S]](LeetCode.playground/Pages/832.%20Flipping%20an%20Image.xcplaygroundpage/Contents.swift) 0832. Flipping an Image \n- [X] 🤨 [[Q]](https://leetcode.com/problems/image-overlap/) [[S]](LeetCode.playground/Pages/835.%20Image%20Overlap.xcplaygroundpage/Contents.swift) 0835. Image Overlap *[Hash Table]*\n- [X] 📝 [[Q]](https://leetcode.com/problems/similar-string-groups/) [[S]](LeetCode.playground/Pages/839-Similar%20String%20Groups.xcplaygroundpage/Contents.swift) 0839. Similar String Groups \n- [X] 🤨 [[Q]](https://leetcode.com/problems/keys-and-rooms/) [[S]](LeetCode.playground/Pages/841.%20Keys%20and%20Rooms.xcplaygroundpage/Contents.swift) 0841. Keys and Rooms *[Graph, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/shifting-letters/) [[S]](LeetCode.playground/Pages/848.%20Shifting%20Letters.xcplaygroundpage/Contents.swift) 0848. Shifting Letters \n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximize-distance-to-closest-person/) [[S]](LeetCode20Q4.playground/Pages/849.%20Maximize%20Distance%20to%20Closest%20Person.xcplaygroundpage/Contents.swift) 0849. Maximize Distance to Closest Person *[O(n)]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/rectangle-area-ii/) [[S]](LeetCode.playground/Pages/850-Rectangle%20Area%20II.xcplaygroundpage/Contents.swift) 0850. Rectangle Area II *[Mathematics]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/minimum-cost-to-hire-k-workers/) [[S]](LeetCode.playground/Pages/857.%20Minimum%20Cost%20to%20Hire%20K%20Workers.xcplaygroundpage/Contents.swift) 0857. Minimum Cost to Hire K Workers *[Heap, Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/buddy-strings/) [[S]](LeetCode20Q4.playground/Pages/859.%20Buddy%20Strings.xcplaygroundpage/Contents.swift) 0859. Buddy Strings *[String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/boats-to-save-people/) [[S]](LeetCode.playground/Pages/881-Boats%20to%20Save%20People.xcplaygroundpage/Contents.swift) 0881. Boats to Save People *[Greedy, Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/possible-bipartition/) [[S]](LeetCode.playground/Pages/886-Possible%20Bipartition.xcplaygroundpage/Contents.swift) 0886. Possible Bipartition *[Graph, DFS]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/super-egg-drop/) [[S]](LeetCode.playground/Pages/887.%20Super%20Egg%20Drop.xcplaygroundpage/Contents.swift) 0887. Super Egg Drop *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/monotonic-array/) [[S]](LeetCode.playground/Pages/896.%20Monotonic%20Array.xcplaygroundpage/Contents.swift) 0896. Monotonic Array \n- [X] 🤨 [[Q]](https://leetcode.com/problems/online-stock-span/) [[S]](LeetCode.playground/Pages/901-Online%20Stock%20Span.xcplaygroundpage/Contents.swift) 0901. Online Stock Span *[Array, Stack]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/sort-array-by-parity/) [[S]](LeetCode.playground/Pages/905.%20Sort%20Array%20By%20Parity.xcplaygroundpage/Contents.swift) 0905. Sort Array By Parity *[Sort, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sort-an-array/) [[S]](LeetCode.playground/Pages/912-Sort%20an%20Array.xcplaygroundpage/Contents.swift) 0912. Sort an Array *[Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/maximum-sum-circular-subarray/) [[S]](LeetCode.playground/Pages/918-Maximum%20Sum%20Circular%20Subarray.xcplaygroundpage/Contents.swift) 0918. Maximum Sum Circular Subarray *[DP]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/number-of-music-playlists/) [[S]](LeetCode.playground/Pages/920.%20Number%20of%20Music%20Playlists.xcplaygroundpage/Contents.swift) 0920. Number of Music Playlists *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-add-to-make-parentheses-valid/) [[S]](LeetCode21Q1.playground/Pages/921.%20Minimum%20Add%20to%20Make%20Parentheses%20Valid.xcplaygroundpage/Contents.swift) 0921. Minimum Add to Make Parentheses Valid *[Stack]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/sort-array-by-parity-ii/) [[S]](LeetCode.playground/Pages/922.%20Sort%20Array%20By%20Parity%20II.xcplaygroundpage/Contents.swift) 0922. Sort Array By Parity II *[Sort, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-falling-path-sum/) [[S]](LeetCode.playground/Pages/931.%20Minimum%20Falling%20Path%20Sum.xcplaygroundpage/Contents.swift) 0931. Minimum Falling Path Sum *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/number-of-recent-calls/) [[S]](LeetCode.playground/Pages/933.%20Number%20of%20Recent%20Calls.xcplaygroundpage/Contents.swift) 0933. Number of Recent Calls *[Binary Search]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/stamping-the-sequence/) [[S]](LeetCode.playground/Pages/936-Stamping%20The%20Sequence.xcplaygroundpage/Contents.swift) 0936. Stamping The Sequence *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/validate-stack-sequences/) [[S]](LeetCode21Q1.playground/Pages/946.%20Validate%20Stack%20Sequences.xcplaygroundpage/Contents.swift) 0946. Validate Stack Sequences *[O(n), Stack]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/bag-of-tokens/) [[S]](LeetCode20Q4.playground/Pages/948.%20Bag%20of%20Tokens.xcplaygroundpage/Contents.swift) 0948. Bag of Tokens *[Two Pointers, O(n), Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/largest-time-for-given-digits/) [[S]](LeetCode.playground/Pages/949.%20Largest%20Time%20for%20Given%20Digits.xcplaygroundpage/Contents.swift) 0949. Largest Time for Given Digits *[String, Mathematics]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/largest-component-size-by-common-factor/) [[S]](LeetCode.playground/Pages/952.%20Largest%20Component%20Size%20by%20Common%20Factor.xcplaygroundpage/Contents.swift) 0952. Largest Component Size by Common Factor *[Mathematics, Union Find]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/prison-cells-after-n-days/) [[S]](LeetCode.playground/Pages/957.%20Prison%20Cells%20After%20N%20Days.xcplaygroundpage/Contents.swift) 0957. Prison Cells After N Days *[Hash Table]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/regions-cut-by-slashes/) [[S]](LeetCode21Q1.playground/Pages/959.%20Regions%20Cut%20By%20Slashes.xcplaygroundpage/Contents.swift) 0959. Regions Cut By Slashes *[Union Find]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/maximum-width-ramp/) [[S]](LeetCode.playground/Pages/962.%20Maximum%20Width%20Ramp.xcplaygroundpage/Contents.swift) 0962. Maximum Width Ramp *[Stack, Two Pointers]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/numbers-with-same-consecutive-differences/) [[S]](LeetCode.playground/Pages/967.%20Numbers%20With%20Same%20Consecutive%20Differences.xcplaygroundpage/Contents.swift) 0967. Numbers With Same Consecutive Differences *[DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/pancake-sorting/) [[S]](LeetCode.playground/Pages/969.%20Pancake%20Sorting.xcplaygroundpage/Contents.swift) 0969. Pancake Sorting *[Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/k-closest-points-to-origin/) [[S]](LeetCode.playground/Pages/973-K%20Closest%20Points%20to%20Origin.xcplaygroundpage/Contents.swift) 0973. K Closest Points to Origin *[Sort]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/subarray-sums-divisible-by-k/) [[S]](LeetCode.playground/Pages/974-Subarray%20Sums%20Divisible%20by%20K.xcplaygroundpage/Contents.swift) 0974. Subarray Sums Divisible by K *[Hash Table]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/longest-turbulent-subarray/) [[S]](LeetCode.playground/Pages/978-Longest%20Turbulent%20Subarray.xcplaygroundpage/Contents.swift) 0978. Longest Turbulent Subarray *[DP, Sliding Windows]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/unique-paths-iii/) [[S]](LeetCode.playground/Pages/980.%20Unique%20Paths%20III.xcplaygroundpage/Contents.swift) 0980. Unique Paths III *[Graph, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-cost-for-tickets/) [[S]](LeetCode.playground/Pages/983.%20Minimum%20Cost%20For%20Tickets.xcplaygroundpage/Contents.swift) 0983. Minimum Cost For Tickets *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/string-without-aaa-or-bbb/) [[S]](LeetCode.playground/Pages/984-String%20Without%20AAA%20or%20BBB.xcplaygroundpage/Contents.swift) 0984. String Without AAA or BBB *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/interval-list-intersections/) [[S]](LeetCode.playground/Pages/986-Interval%20List%20Intersections.xcplaygroundpage/Contents.swift) 0986. Interval List Intersections *[Two Pointers, Greedy]*\n- [X] 🤬 [[Q]](https://leetcode.com/problems/vertical-order-traversal-of-a-binary-tree/) [[S]](LeetCode.playground/Pages/987.%20Vertical%20Order%20Traversal%20of%20a%20Binary%20Tree.xcplaygroundpage/Contents.swift) 0987. Vertical Order Traversal of a Binary Tree *[Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/satisfiability-of-equality-equations/) [[S]](LeetCode.playground/Pages/990-Satisfiability%20of%20Equality%20Equations.xcplaygroundpage/Contents.swift) 0990. Satisfiability of Equality Equations *[Union Find]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/broken-calculator/) [[S]](LeetCode21Q1.playground/Pages/991.%20Broken%20Calculator.xcplaygroundpage/Contents.swift) 0991. Broken Calculator *[Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/cousins-in-binary-tree/) [[S]](LeetCode.playground/Pages/993-Cousins%20in%20Binary%20Tree.xcplaygroundpage/Contents.swift) 0993. Cousins in Binary Tree *[Tree, DFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/rotting-oranges/) [[S]](LeetCode.playground/Pages/994.%20Rotting%20Oranges.xcplaygroundpage/Contents.swift) 0994. Rotting Oranges *[Graph, BFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/find-the-town-judge/) [[S]](LeetCode.playground/Pages/997-Find%20the%20Town%20Judge.xcplaygroundpage/Contents.swift) 0997. Find the Town Judge *[Graph]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-domino-rotations-for-equal-row/) [[S]](LeetCode20Q4.playground/Pages/1007.%20Minimum%20Domino%20Rotations%20For%20Equal%20Row.xcplaygroundpage/Contents.swift) 1007. Minimum Domino Rotations For Equal Row \n- [X] 🤨 [[Q]](https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal/) [[S]](LeetCode.playground/Pages/1008-Construct%20Binary%20Search%20Tree%20from%20Preorder%20Traversal.xcplaygroundpage/Contents.swift) 1008. Construct Binary Search Tree from Preorder Traversal *[Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/complement-of-base-10-integer/) [[S]](LeetCode.playground/Pages/1009-Complement%20of%20Base%2010%20Integer.xcplaygroundpage/Contents.swift) 1009. Complement of Base 10 Integer *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/smallest-integer-divisible-by-k/) [[S]](LeetCode20Q4.playground/Pages/1015.%20Smallest%20Integer%20Divisible%20by%20K.xcplaygroundpage/Contents.swift) 1015. Smallest Integer Divisible by K \n- [X] 😊 [[Q]](https://leetcode.com/problems/remove-outermost-parentheses/) [[S]](LeetCode.playground/Pages/1021.%20Remove%20Outermost%20Parentheses.xcplaygroundpage/Contents.swift) 1021. Remove Outermost Parentheses *[Stack]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/sum-of-root-to-leaf-binary-numbers/) [[S]](LeetCode.playground/Pages/1022.%20Sum%20of%20Root%20To%20Leaf%20Binary%20Numbers.xcplaygroundpage/Contents.swift) 1022. Sum of Root To Leaf Binary Numbers *[Tree, DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/divisor-game/) [[S]](LeetCode.playground/Pages/1025.%20Divisor%20Game.xcplaygroundpage/Contents.swift) 1025. Divisor Game *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/two-city-scheduling/) [[S]](LeetCode.playground/Pages/1029-Two%20City%20Scheduling.xcplaygroundpage/Contents.swift) 1029. Two City Scheduling *[Greedy]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/stream-of-characters/) [[S]](LeetCode.playground/Pages/1032.%20Stream%20of%20Characters.xcplaygroundpage/Contents.swift) 1032. Stream of Characters *[Tree, String]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/uncrossed-lines/) [[S]](LeetCode.playground/Pages/1035-Uncrossed%20Lines.xcplaygroundpage/Contents.swift) 1035. Uncrossed Lines *[DP]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/robot-bounded-in-circle/) [[S]](LeetCode.playground/Pages/1041.%20Robot%20Bounded%20In%20Circle.xcplaygroundpage/Contents.swift) 1041. Robot Bounded In Circle \n- [X] 🤨 [[Q]](https://leetcode.com/problems/partition-array-for-maximum-sum/) [[S]](LeetCode.playground/Pages/1043.%20Partition%20Array%20for%20Maximum%20Sum.xcplaygroundpage/Contents.swift) 1043. Partition Array for Maximum Sum *[DP]*\n- [X] 🤬 [[Q]](https://leetcode.com/problems/longest-duplicate-substring/) [[S]](LeetCode.playground/Pages/1044.%20Longest%20Duplicate%20Substring.xcplaygroundpage/Contents.swift) 1044. Longest Duplicate Substring *[Hash Table, Sliding Windows, String, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/largest-values-from-labels/) [[S]](LeetCode.playground/Pages/1090.%20Largest%20Values%20From%20Labels.xcplaygroundpage/Contents.swift) 1090. Largest Values From Labels *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/car-pooling/) [[S]](LeetCode.playground/Pages/1094.%20Car%20Pooling.xcplaygroundpage/Contents.swift) 1094. Car Pooling *[Array]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/distribute-candies-to-people/) [[S]](LeetCode.playground/Pages/1103.%20Distribute%20Candies%20to%20People.xcplaygroundpage/Contents.swift) 1103. Distribute Candies to People \n- [X] 😊 [[Q]](https://leetcode.com/problems/defanging-an-ip-address/) [[S]](LeetCode.playground/Pages/1108-Defanging%20an%20IP%20Address.xcplaygroundpage/Contents.swift) 1108. Defanging an IP Address \n- [X] 😊 [[Q]](https://leetcode.com/problems/relative-sort-array/) [[S]](LeetCode.playground/Pages/1122.%20Relative%20Sort%20Array.xcplaygroundpage/Contents.swift) 1122. Relative Sort Array *[Hash Table, Sort]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/minimum-absolute-difference/) [[S]](LeetCode.playground/Pages/1200.%20Minimum%20Absolute%20Difference.xcplaygroundpage/Contents.swift) 1200. Minimum Absolute Difference \n- [X] 🔞 [[Q]](https://leetcode.com/problems/sort-items-by-groups-respecting-dependencies/) [[S]](LeetCode.playground/Pages/1203.%20Sort%20Items%20by%20Groups%20Respecting%20Dependencies.xcplaygroundpage/Contents.swift) 1203. Sort Items by Groups Respecting Dependencies *[Graph, DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/minimum-cost-to-move-chips-to-the-same-position/) [[S]](LeetCode20Q4.playground/Pages/1217.%20Minimum%20Cost%20to%20Move%20Chips%20to%20The%20Same%20Position.xcplaygroundpage/Contents.swift) 1217. Minimum Cost to Move Chips to The Same Position \n- [X] 😊 [[Q]](https://leetcode.com/problems/split-a-string-in-balanced-strings/) [[S]](LeetCode.playground/Pages/1221.%20Split%20a%20String%20in%20Balanced%20Strings.xcplaygroundpage/Contents.swift) 1221. Split a String in Balanced Strings \n- [X] 😊 [[Q]](https://leetcode.com/problems/check-if-it-is-a-straight-line/) [[S]](LeetCode.playground/Pages/1232-Check%20If%20It%20Is%20a%20Straight%20Line.xcplaygroundpage/Contents.swift) 1232. Check If It Is a Straight Line *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-sub-folders-from-the-filesystem/) [[S]](LeetCode.playground/Pages/1233.%20Remove%20Sub-Folders%20from%20the%20Filesystem.xcplaygroundpage/Contents.swift) 1233. Remove Sub-Folders from the Filesystem *[Tree, DFS, String, Binary Search]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/maximum-profit-in-job-scheduling/) [[S]](LeetCode.playground/Pages/1235.%20Maximum%20Profit%20in%20Job%20Scheduling.xcplaygroundpage/Contents.swift) 1235. Maximum Profit in Job Scheduling *[DP, Binary Search]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses/) [[S]](LeetCode21Q1.playground/Pages/1249.%20Minimum%20Remove%20to%20Make%20Valid%20Parentheses.xcplaygroundpage/Contents.swift) 1249. Minimum Remove to Make Valid Parentheses *[O(n), Stack, String]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/check-if-it-is-a-good-array/) [[S]](LeetCode.playground/Pages/1250.%20Check%20If%20It%20Is%20a%20Good%20Array.xcplaygroundpage/Contents.swift) 1250. Check If It Is a Good Array *[Mathematics]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/minimum-moves-to-move-a-box-to-their-target-location/) [[S]](LeetCode.playground/Pages/1263-Minimum%20Moves%20to%20Move%20a%20Box%20to%20Their%20Target%20Location.xcplaygroundpage/Contents.swift) 1263. Minimum Moves to Move a Box to Their Target Location *[Graph, BFS, Shortest Path]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/minimum-time-visiting-all-points/) [[S]](LeetCode.playground/Pages/1266.%20Minimum%20Time%20Visiting%20All%20Points%20copy.xcplaygroundpage/Contents.swift) 1266. Minimum Time Visiting All Points \n- [X] 🔞 [[Q]](https://leetcode.com/problems/count-square-submatrices-with-all-ones/) [[S]](LeetCode.playground/Pages/1277-Count%20Square%20Submatrices%20with%20All%20Ones.xcplaygroundpage/Contents.swift) 1277. Count Square Submatrices with All Ones *[DP]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/palindrome-partitioning-iii/) [[S]](LeetCode.playground/Pages/1278-Palindrome%20Partitioning%20III.xcplaygroundpage/Contents.swift) 1278. Palindrome Partitioning III *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/subtract-the-product-and-sum-of-digits-of-an-integer/) [[S]](LeetCode.playground/Pages/1281.%20Subtract%20the%20Product%20and%20Sum%20of%20Digits%20of%20an%20Integer.xcplaygroundpage/Contents.swift) 1281. Subtract the Product and Sum of Digits of an Integer \n- [X] 🤨 [[Q]](https://leetcode.com/problems/group-the-people-given-the-group-size-they-belong-to/) [[S]](LeetCode.playground/Pages/1282.%20Group%20the%20People%20Given%20the%20Group%20Size%20They%20Belong%20To.xcplaygroundpage/Contents.swift) 1282. Group the People Given the Group Size They Belong To \n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-the-smallest-divisor-given-a-threshold/) [[S]](LeetCode20Q4.playground/Pages/1283.%20Find%20the%20Smallest%20Divisor%20Given%20a%20Threshold.xcplaygroundpage/Contents.swift) 1283. Find the Smallest Divisor Given a Threshold \n- [X] 🤨 [[Q]](https://leetcode.com/problems/iterator-for-combination/) [[S]](LeetCode.playground/Pages/1286.%20Iterator%20for%20Combination.xcplaygroundpage/Contents.swift) 1286. Iterator for Combination *[Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/remove-covered-intervals/) [[S]](LeetCode.playground/Pages/1288.%20Remove%20Covered%20Intervals.xcplaygroundpage/Contents.swift) 1288. Remove Covered Intervals *[Greedy, Sort]*\n- [X] 📝 [[Q]](https://leetcode.com/problems/minimum-falling-path-sum-ii/) [[S]](LeetCode.playground/Pages/1289.%20Minimum%20Falling%20Path%20Sum%20II.xcplaygroundpage/Contents.swift) 1289. Minimum Falling Path Sum II *[DP]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/) [[S]](LeetCode.playground/Pages/1290.%20Convert%20Binary%20Number%20in%20a%20Linked%20List%20to%20Integer.xcplaygroundpage/Contents.swift) 1290. Convert Binary Number in a Linked List to Integer *[Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/sequential-digits/) [[S]](LeetCode.playground/Pages/1291.%20Sequential%20Digits.xcplaygroundpage/Contents.swift) 1291. Sequential Digits *[DFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/find-numbers-with-even-number-of-digits/) [[S]](LeetCode.playground/Pages/1295.%20Find%20Numbers%20with%20Even%20Number%20of%20Digits.xcplaygroundpage/Contents.swift) 1295. Find Numbers with Even Number of Digits \n- [X] 😊 [[Q]](https://leetcode.com/problems/replace-elements-with-greatest-element-on-right-side/) [[S]](LeetCode.playground/Pages/1299.%20Replace%20Elements%20with%20Greatest%20Element%20on%20Right%20Side.xcplaygroundpage/Contents.swift) 1299. Replace Elements with Greatest Element on Right Side \n- [X] 🤨 [[Q]](https://leetcode.com/problems/all-elements-in-two-binary-search-trees/) [[S]](LeetCode.playground/Pages/1305.%20All%20Elements%20in%20Two%20Binary%20Search%20Trees.xcplaygroundpage/Contents.swift) 1305. All Elements in Two Binary Search Trees *[Tree]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/jump-game-iii/) [[S]](LeetCode.playground/Pages/1306-Jump%20Game%20III.xcplaygroundpage/Contents.swift) 1306. Jump Game III *[BFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/decrypt-string-from-alphabet-to-integer-mapping/) [[S]](LeetCode.playground/Pages/1309.%20Decrypt%20String%20from%20Alphabet%20to%20Integer%20Mapping.xcplaygroundpage/Contents.swift) 1309. Decrypt String from Alphabet to Integer Mapping \n- [X] 😊 [[Q]](https://leetcode.com/problems/decompress-run-length-encoded-list/) [[S]](LeetCode.playground/Pages/1313.%20Decompress%20Run-Length%20Encoded%20List.xcplaygroundpage/Contents.swift) 1313. Decompress Run-Length Encoded List \n- [X] 🤨 [[Q]](https://leetcode.com/problems/number-of-operations-to-make-network-connected/) [[S]](LeetCode.playground/Pages/1319-Number%20of%20Operations%20to%20Make%20Network%20Connected.xcplaygroundpage/Contents.swift) 1319. Number of Operations to Make Network Connected *[Graph, Union Find]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/reverse-subarray-to-maximize-array-value/) [[S]](LeetCode.playground/Pages/1330.%20Reverse%20Subarray%20To%20Maximize%20Array%20Value.xcplaygroundpage/Contents.swift) 1330. Reverse Subarray To Maximize Array Value *[Mathematics, O(n)]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/find-the-city-with-the-smallest-number-of-neighbors-at-a-threshold-distance/) [[S]](LeetCode.playground/Pages/1334-Find%20the%20City.xcplaygroundpage/Contents.swift) 1334. Find the City With the Smallest Number of Neighbors at a Threshold Distance *[Graph, Shortest Path]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/) [[S]](LeetCode21Q1.playground/Pages/1337.%20The%20K%20Weakest%20Rows%20in%20a%20Matrix.xcplaygroundpage/Contents.swift) 1337. The K Weakest Rows in a Matrix *[Binary Search]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/number-of-steps-to-reduce-a-number-to-zero/) [[S]](LeetCode.playground/Pages/1342-Number%20of%20Steps%20to%20Reduce%20a%20Number%20to%20Zero.xcplaygroundpage/Contents.swift) 1342. Number of Steps to Reduce a Number to Zero \n- [X] 🤨 [[Q]](https://leetcode.com/problems/angle-between-hands-of-a-clock/) [[S]](LeetCode.playground/Pages/1344.%20Angle%20Between%20Hands%20of%20a%20Clock.xcplaygroundpage/Contents.swift) 1344. Angle Between Hands of a Clock \n- [X] 😫 [[Q]](https://leetcode.com/problems/jump-game-iv/) [[S]](LeetCode.playground/Pages/1345.%20Jump%20Game%20IV.xcplaygroundpage/Contents.swift) 1345. Jump Game IV *[BFS]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/count-negative-numbers-in-a-sorted-matrix/) [[S]](LeetCode.playground/Pages/1351.%20Count%20Negative%20Numbers%20in%20a%20Sorted%20Matrix.xcplaygroundpage/Contents.swift) 1351. Count Negative Numbers in a Sorted Matrix \n- [X] 😫 [[Q]](https://leetcode.com/problems/largest-multiple-of-three/) [[S]](LeetCode.playground/Pages/1363.%20Largest%20Multiple%20of%20Three.xcplaygroundpage/Contents.swift) 1363. Largest Multiple of Three *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/) [[S]](LeetCode.playground/Pages/1365.%20How%20Many%20Numbers%20Are%20Smaller%20Than%20the%20Current%20Number.xcplaygroundpage/Contents.swift) 1365. How Many Numbers Are Smaller Than the Current Number \n- [X] 🤨 [[Q]](https://leetcode.com/problems/linked-list-in-binary-tree/) [[S]](LeetCode.playground/Pages/1367.%20Linked%20List%20in%20Binary%20Tree.xcplaygroundpage/Contents.swift) 1367. Linked List in Binary Tree *[Tree, DFS]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/minimum-cost-to-make-at-least-one-valid-path-in-a-grid/) [[S]](LeetCode.playground/Pages/1368.%20Minimum%20Cost%20to%20Make%20at%20Least%20One%20Valid%20Path%20in%20a%20Grid.xcplaygroundpage/Contents.swift) 1368. Minimum Cost to Make at Least One Valid Path in a Grid *[Graph, Shortest Path]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/cinema-seat-allocation/) [[S]](LeetCode.playground/Pages/1386.%20Cinema%20Seat%20Allocation.xcplaygroundpage/Contents.swift) 1386. Cinema Seat Allocation *[Greedy]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/check-if-there-is-a-valid-path-in-a-grid/) [[S]](LeetCode.playground/Pages/1391.%20Check%20if%20There%20is%20a%20Valid%20Path%20in%20a%20Grid.xcplaygroundpage/Contents.swift) 1391. Check if There is a Valid Path in a Grid *[Graph, BFS]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/count-number-of-teams/) [[S]](LeetCode.playground/Pages/1395-Count%20Number%20of%20Teams.xcplaygroundpage/Contents.swift) 1395. Count Number of Teams *[Mathematics]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/number-of-steps-to-reduce-a-number-in-binary-representation-to-one/) [[S]](LeetCode.playground/Pages/1404.%20Number%20of%20Steps%20to%20Reduce%20a%20Number%20in%20Binary%20Representation%20to%20One.xcplaygroundpage/Contents.swift) 1404. Number of Steps to Reduce a Number in Binary Representation to One *[O(n), Bit Manipulation]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/longest-happy-string/) [[S]](LeetCode.playground/Pages/1405-Longest%20Happy%20String.xcplaygroundpage/Contents.swift) 1405. Longest Happy String *[Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/kids-with-the-greatest-number-of-candies/) [[S]](LeetCode.playground/Pages/1431-Kids%20With%20the%20Greatest%20Number%20of%20Candies.xcplaygroundpage/Contents.swift) 1431. Kids With the Greatest Number of Candies *[Array]*\n- [X] 🤨 [[Q]](https://leetcode.com/problems/max-difference-you-can-get-from-changing-an-integer/) [[S]](LeetCode.playground/Pages/1432.%20Max%20Difference%20You%20Can%20Get%20From%20Changing%20an%20Integer.xcplaygroundpage/Contents.swift) 1432. Max Difference You Can Get From Changing an Integer *[Mathematics, Greedy]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/destination-city/) [[S]](LeetCode.playground/Pages/1436.%20Destination%20City.xcplaygroundpage/Contents.swift) 1436. Destination City *[Hash Table, Graph]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/consecutive-characters/) [[S]](LeetCode20Q4.playground/Pages/1446.%20Consecutive%20Characters.xcplaygroundpage/Contents.swift) 1446. Consecutive Characters \n- [X] 😊 [[Q]](https://leetcode.com/problems/number-of-students-doing-homework-at-a-given-time/) [[S]](LeetCode.playground/Pages/1450.%20Number%20of%20Students%20Doing%20Homework%20at%20a%20Given%20Time.xcplaygroundpage/Contents.swift) 1450. Number of Students Doing Homework at a Given Time \n- [X] 🤨 [[Q]](https://leetcode.com/problems/pseudo-palindromic-paths-in-a-binary-tree/) [[S]](LeetCode.playground/Pages/1457.%20Pseudo-Palindromic%20Paths%20in%20a%20Binary%20Tree.xcplaygroundpage/Contents.swift) 1457. Pseudo-Palindromic Paths in a Binary Tree *[Bit Manipulation, Tree]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/maximum-product-of-two-elements-in-an-array/) [[S]](LeetCode.playground/Pages/1464-Maximum%20Product%20of%20Two%20Elements%20in%20an%20Array.xcplaygroundpage/Contents.swift) 1464. Maximum Product of Two Elements in an Array *[Mathematics]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/final-prices-with-a-special-discount-in-a-shop/) [[S]](LeetCode.playground/Pages/1475.%20Final%20Prices%20With%20a%20Special%20Discount%20in%20a%20Shop.xcplaygroundpage/Contents.swift) 1475. Final Prices With a Special Discount in a Shop *[Stack, O(n)]*\n- [X] 🔞 [[Q]](https://leetcode.com/problems/parallel-courses-ii/) [[S]](LeetCode21Q1.playground/Pages/1494.%20Parallel%20Courses%20II.xcplaygroundpage/Contents.swift) 1494. Parallel Courses II *[DP, Bit Manipulation, NP Complete]*\n- [X] 😊 [[Q]](https://leetcode.com/problems/path-crossing/) [[S]](LeetCode.playground/Pages/1496.%20Path%20Crossing.xcplaygroundpage/Contents.swift) 1496. Path Crossing *[Hash Table]*\n- [X] 😫 [[Q]](https://leetcode.com/problems/stone-game-iv/) [[S]](LeetCode20Q4.playground/Pages/1510.%20Stone%20Game%20IV.xcplaygroundpage/Contents.swift) 1510. Stone Game IV *[DP]*\n\n\u003cdetails\u003e\n\u003csummary\u003eTodo\u003c/summary\u003e\n\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/4sum/) ~~[S]~~ 0018. 4Sum\n- [ ] 😫 [[Q]](https://leetcode.com/problems/substring-with-concatenation-of-all-words/) ~~[S]~~ 0030. Substring with Concatenation of All Words\n- [ ] 😫 [[Q]](https://leetcode.com/problems/sudoku-solver/) ~~[S]~~ 0037. Sudoku Solver\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/permutations-ii/) ~~[S]~~ 0047. Permutations II\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/group-anagrams/) ~~[S]~~ 0049. Group Anagrams\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/spiral-matrix/) ~~[S]~~ 0054. Spiral Matrix\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/spiral-matrix-ii/) ~~[S]~~ 0059. Spiral Matrix II\n- [ ] 😫 [[Q]](https://leetcode.com/problems/text-justification/) ~~[S]~~ 0068. Text Justification\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/set-matrix-zeroes/) ~~[S]~~ 0073. Set Matrix Zeroes\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/combinations/) ~~[S]~~ 0077. Combinations\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/word-search/) ~~[S]~~ 0079. Word Search\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/search-in-rotated-sorted-array-ii/) ~~[S]~~ 0081. Search in Rotated Sorted Array II\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/) ~~[S]~~ 0082. Remove Duplicates from Sorted List II\n- [ ] 😊 [[Q]](https://leetcode.com/problems/remove-duplicates-from-sorted-list/) ~~[S]~~ 0083. Remove Duplicates from Sorted List\n- [ ] 😫 [[Q]](https://leetcode.com/problems/largest-rectangle-in-histogram/) ~~[S]~~ 0084. Largest Rectangle in Histogram\n- [ ] 😫 [[Q]](https://leetcode.com/problems/maximal-rectangle/) ~~[S]~~ 0085. Maximal Rectangle\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/partition-list/) ~~[S]~~ 0086. Partition List\n- [ ] 😊 [[Q]](https://leetcode.com/problems/merge-sorted-array/) ~~[S]~~ 0088. Merge Sorted Array\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/gray-code/) ~~[S]~~ 0089. Gray Code\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/restore-ip-addresses/) ~~[S]~~ 0093. Restore IP Addresses\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-inorder-traversal/) ~~[S]~~ 0094. Binary Tree Inorder Traversal\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/unique-binary-search-trees-ii/) ~~[S]~~ 0095. Unique Binary Search Trees II\n- [ ] 😊 [[Q]](https://leetcode.com/problems/symmetric-tree/) ~~[S]~~ 0101. Symmetric Tree\n- [ ] 😊 [[Q]](https://leetcode.com/problems/maximum-depth-of-binary-tree/) ~~[S]~~ 0104. Maximum Depth of Binary Tree\n- [ ] 😊 [[Q]](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) ~~[S]~~ 0108. Convert Sorted Array to Binary Search Tree\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/) ~~[S]~~ 0109. Convert Sorted List to Binary Search Tree\n- [ ] 😊 [[Q]](https://leetcode.com/problems/balanced-binary-tree/) ~~[S]~~ 0110. Balanced Binary Tree\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/) ~~[S]~~ 0114. Flatten Binary Tree to Linked List\n- [ ] 😫 [[Q]](https://leetcode.com/problems/distinct-subsequences/) ~~[S]~~ 0115. Distinct Subsequences\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/) ~~[S]~~ 0116. Populating Next Right Pointers in Each Node\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/) ~~[S]~~ 0117. Populating Next Right Pointers in Each Node II\n- [ ] 😫 [[Q]](https://leetcode.com/problems/binary-tree-maximum-path-sum/) ~~[S]~~ 0124. Binary Tree Maximum Path Sum\n- [ ] 😫 [[Q]](https://leetcode.com/problems/word-ladder-ii/) ~~[S]~~ 0126. Word Ladder II\n- [ ] 😫 [[Q]](https://leetcode.com/problems/longest-consecutive-sequence/) ~~[S]~~ 0128. Longest Consecutive Sequence\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-preorder-traversal/) ~~[S]~~ 0144. Binary Tree Preorder Traversal\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-postorder-traversal/) ~~[S]~~ 0145. Binary Tree Postorder Traversal\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/lru-cache/) ~~[S]~~ 0146. LRU Cache\n- [ ] 😫 [[Q]](https://leetcode.com/problems/max-points-on-a-line/) ~~[S]~~ 0149. Max Points on a Line\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/evaluate-reverse-polish-notation/) ~~[S]~~ 0150. Evaluate Reverse Polish Notation\n- [ ] 😊 [[Q]](https://leetcode.com/problems/min-stack/) ~~[S]~~ 0155. Min Stack\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/binary-tree-upside-down/) ~~[S]~~ 0156. Binary Tree Upside Down\n- [ ] 😊 [[Q]](https://leetcode.com/problems/read-n-characters-given-read4/) ~~[S]~~ 0157. Read N Characters Given Read4\n- [ ] 😫 [[Q]](https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/) ~~[S]~~ 0158. Read N Characters Given Read4 II - Call multiple times\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/) ~~[S]~~ 0159. Longest Substring with At Most Two Distinct Characters\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/one-edit-distance/) ~~[S]~~ 0161. One Edit Distance\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/find-peak-element/) ~~[S]~~ 0162. Find Peak Element\n- [ ] 😊 [[Q]](https://leetcode.com/problems/missing-ranges/) ~~[S]~~ 0163. Missing Ranges\n- [ ] 😫 [[Q]](https://leetcode.com/problems/maximum-gap/) ~~[S]~~ 0164. Maximum Gap\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/fraction-to-recurring-decimal/) ~~[S]~~ 0166. Fraction to Recurring Decimal\n- [ ] 😊 [[Q]](https://leetcode.com/problems/excel-sheet-column-title/) ~~[S]~~ 0168. Excel Sheet Column Title\n- [ ] 😊 [[Q]](https://leetcode.com/problems/two-sum-iii-data-structure-design/) ~~[S]~~ 0170. Two Sum III - Data structure design\n- [ ] 😊 [[Q]](https://leetcode.com/problems/factorial-trailing-zeroes/) ~~[S]~~ 0172. Factorial Trailing Zeroes\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/binary-search-tree-iterator/) ~~[S]~~ 0173. Binary Search Tree Iterator\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/reverse-words-in-a-string-ii/) ~~[S]~~ 0186. Reverse Words in a String II\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/number-of-islands/) ~~[S]~~ 0200. Number of Islands\n- [ ] 😊 [[Q]](https://leetcode.com/problems/happy-number/) ~~[S]~~ 0202. Happy Number\n- [ ] 😊 [[Q]](https://leetcode.com/problems/isomorphic-strings/) ~~[S]~~ 0205. Isomorphic Strings\n- [ ] 😫 [[Q]](https://leetcode.com/problems/word-search-ii/) ~~[S]~~ 0212. Word Search II\n- [ ] 😫 [[Q]](https://leetcode.com/problems/shortest-palindrome/) ~~[S]~~ 0214. Shortest Palindrome\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/kth-largest-element-in-an-array/) ~~[S]~~ 0215. Kth Largest Element in an Array\n- [ ] 😫 [[Q]](https://leetcode.com/problems/the-skyline-problem/) ~~[S]~~ 0218. The Skyline Problem\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/maximal-square/) ~~[S]~~ 0221. Maximal Square\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/rectangle-area/) ~~[S]~~ 0223. Rectangle Area\n- [ ] 😫 [[Q]](https://leetcode.com/problems/basic-calculator/) ~~[S]~~ 0224. Basic Calculator\n- [ ] 😊 [[Q]](https://leetcode.com/problems/implement-stack-using-queues/) ~~[S]~~ 0225. Implement Stack using Queues\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/basic-calculator-ii/) ~~[S]~~ 0227. Basic Calculator II\n- [ ] 😊 [[Q]](https://leetcode.com/problems/implement-queue-using-stacks/) ~~[S]~~ 0232. Implement Queue using Stacks\n- [ ] 😫 [[Q]](https://leetcode.com/problems/number-of-digit-one/) ~~[S]~~ 0233. Number of Digit One\n- [ ] 😊 [[Q]](https://leetcode.com/problems/palindrome-linked-list/) ~~[S]~~ 0234. Palindrome Linked List\n- [ ] 😊 [[Q]](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/) ~~[S]~~ 0235. Lowest Common Ancestor of a Binary Search Tree\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) ~~[S]~~ 0236. Lowest Common Ancestor of a Binary Tree\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/product-of-array-except-self/) ~~[S]~~ 0238. Product of Array Except Self\n- [ ] 😫 [[Q]](https://leetcode.com/problems/sliding-window-maximum/) ~~[S]~~ 0239. Sliding Window Maximum\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/different-ways-to-add-parentheses/) ~~[S]~~ 0241. Different Ways to Add Parentheses\n- [ ] 😊 [[Q]](https://leetcode.com/problems/shortest-word-distance/) ~~[S]~~ 0243. Shortest Word Distance\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/shortest-word-distance-ii/) ~~[S]~~ 0244. Shortest Word Distance II\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/shortest-word-distance-iii/) ~~[S]~~ 0245. Shortest Word Distance III\n- [ ] 😊 [[Q]](https://leetcode.com/problems/strobogrammatic-number/) ~~[S]~~ 0246. Strobogrammatic Number\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/strobogrammatic-number-ii/) ~~[S]~~ 0247. Strobogrammatic Number II\n- [ ] 😫 [[Q]](https://leetcode.com/problems/strobogrammatic-number-iii/) ~~[S]~~ 0248. Strobogrammatic Number III\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/group-shifted-strings/) ~~[S]~~ 0249. Group Shifted Strings\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/count-univalue-subtrees/) ~~[S]~~ 0250. Count Univalue Subtrees\n- [ ] 🤨 [[Q]](https://leetcode.com/problems/flatten-2d-vector/) ~~[S]~~ 0251. Flatten 2","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fbugenzhao%2Fleetcode.playground","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fbugenzhao%2Fleetcode.playground","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fbugenzhao%2Fleetcode.playground/lists"}