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Disclaimer: 这里的题目跟具体的面试毫无关系, 也没有任何指向性; 这些题目是我当年在努力刷题的过程中积累下来的经验和总结!

简介

这个站点已经开启超过7年, 很高兴它可以帮到有需要的人. 信息有价, 知识无价, 每逢闲暇, 我会来维护这个repo, 给刷题的朋友们一些我的想法和见解. 下面来简单介绍一下:

  • README.md: 所有所做过的题目
  • ReviewPage.md: 所有题目的总结和归纳（不断完善中）
  • KnowledgeHash2.md: 对所做过的知识点的一些笔记
  • SystemDesign.md: 对系统设计的一些笔记

001 | about 土汪

tuwangbrick.substack.com 是2022年开启的一个news letter周刊, 每周一更新, 内容是一些工作上遇到的思考, 介绍些遇到的新工具, 偶尔吐槽. 欢迎大家订阅我的周刊. 或者订阅RSS Feed: https://tuwangbrick.substack.com/feed.

○ 📅 欢迎大家在Calendly上跟我约时间1:1, 聊工作生活

○ 👨‍💻 Social Media: YouTube, 小红书, B站, Twitter

○ 🎙 Podcast: 土汪遛弯儿 (小宇宙, Spotify, Apple Podcast)

○ 💬 Chat: 微信 TuwangZ, Discord - tuwang

Youtube 频道: 土汪遛弯儿未来会持续更新在北美科技行业工作的故事和经验. 有任何程序员工作的疑问, 可以加入上面的discord留言.

希望大家学习顺利, 对未来充满希望!

002 | 目录 Java Algorithm Problems

Leetcode# Problem Level Tags Time Space Language Sequence
N/A Jump Game II.java Hard [Array, Coordinate DP, DP, Greedy] O(n) O(1) Java 0
N/A Majority Number II.java Medium [Enumeration, Greedy] Java 1
N/A Search a 2D Matrix II.java Medium [Binary Search, Divide and Conquer] Java 2
N/A Missing Ranges.java Medium [Array] Java 3
N/A Inorder Successor in BST.java Medium [BST, Tree] Java 4
N/A Convert Integer A to Integer B.java Easy [Bit Manipulation] Java 5
N/A Backpack VI.java Medium [Backpack DP, DP] Java 6
N/A Total Occurrence of Target.java Medium [] Java 7
N/A House Robber III.java Medium [DFS, DP, Status DP, Tree] Java 8
N/A Binary Tree Maximum Path Sum II.java Medium [DFS, Tree] Java 9
N/A Backpack V.java Medium [Backpack DP, DP] Java 10
N/A Closest Number in Sorted Array.java Easy [Binary Search] Java 11
N/A Convert Expression to Polish Notation.java Hard [Binary Tree, DFS, Expression Tree, Stack] Java 12
N/A Missing Number.java Easy [Array, Bit Manipulation, Math] Java 13
N/A Restore IP Addresses.java Medium [Backtracking, DFS, String] Java 14
N/A Linked List Cycle II.java Medium [Linked List, Math, Two Pointers] Java 15
N/A Unique Binary Search Tree.java Medium [BST, DP, Tree] Java 16
N/A Largest Number.java Medium [Sort] Java 17
N/A Reverse String.java Easy [String, Two Pointers] Java 18
N/A Triangles.java Medium [Array, Coordinate DP, DFS, DP, Memoization] Java 19
N/A Frog Jump.java Hard [DP, Hash Table] Java 20
N/A Summary Ranges.java Medium [Array] Java 21
N/A Sliding Window Median.java Hard [Design, Heap, MaxHeap, MinHeap, Sliding Window] Java 22
N/A Single Number III.java Medium [Bit Manipulation] Java 23
N/A Trailing Zeros.java Easy [Math] Java 24
N/A Fast Power.java Medium [DFS, Divide and Conquer] Java 25
N/A Perfect Rectangle.java Hard [Design, Geometry, Hash Table] Java 26
N/A Total Hamming Distance.java Medium [Bit Manipulation] O(n) O(1), 32-bit array Java 27
N/A Word Pattern.java Easy [] Java 28
N/A Two Sum IV - Input is a BST.java Easy [Tree] Java 29
N/A Count 1 in Binary.java Easy [Bit Manipulation] Java 30
N/A Two Lists Sum.java Medium [Linked List] Java 31
N/A Flatten 2D Vector.java Medium [Design] Java 32
N/A Hamming Distance.java Easy [] Java 33
N/A Find the Weak Connected Component in the Directed Graph.java Medium [Union Find] Java 34
N/A Interval Minimum Number.java Medium [Binary Search, Divide and Conquer, Lint, Segment Tree] Java 35
N/A Stone Game.java Medium [DP] Java 36
N/A Longest Increasing Continuous subsequence II.java Medium [Array, Coordinate DP, DP, Memoization] Java 37
N/A Plus One.java Easy [Array, Math] Java 38
N/A Paint Fence.java Easy [DP, Sequence DP] O(n) O(n) Java 39
N/A Line Reflection.java Medium [Hash Table, Math] O(n) O(n) Java 40
N/A Binary Representation.java Hard [Bit Manipulation, String] Java 41
N/A Longest Consecutive Sequence.java Hard [Array, Hash Table, Union Find] Java 42
N/A Find Minimum in Rotated Sorted Array.java Medium [Array, Binary Search] Java 43
N/A Binary Tree Longest Consecutive Sequence II.java Medium [DFS, Divide and Conquer, Double Recursive, Tree] Java 44
N/A Minimum Subarray.java Easy [Array, DP, Greedy, Sequence DP, Subarray] O(m) O(1) Java 45
N/A Connecting Graph.java Medium [Union Find] Java 46
N/A Count of Smaller Number.java Medium [Binary Search, Lint, Segment Tree] Java 47
N/A Binary Gap.java Easy [Bit Manipulation] O(n), n = # of bits O(1) Java 48
N/A Flip Game II.java Medium [Backtracking, DFS, DP] Java 49
N/A Subtree of Another Tree.java Easy [DFS, Divide and Conquer, Tree] Java 50
N/A Binary Tree Level Order Traversal II.java Medium [BFS, Tree] Java 51
N/A Maximum Average Subarray I.java Easy [Array, Subarray] O(n) O(1) Java 52
N/A IndexMatch.java Easy [] Java 53
N/A Walls and Gates.java Medium [BFS, DFS] Java 54
N/A Decode String.java Medium [DFS, Divide and Conquer, Stack] Java 55
N/A The Maze.java Medium [BFS, DFS] Java 56
N/A Palindromic Substrings.java Medium [DP, String] Java 57
N/A Rearrange String k Distance Apart.java Hard [Greedy, Hash Table, Heap] Java 58
N/A Count and Say.java Easy [Basic Implementation, String] Java 59
N/A Median of Two Sorted Arrays.java Hard [Array, Binary Search, DFS, Divide and Conquer] Java 60
N/A Perfect Squares.java Medium [BFS, DP, Math, Partition DP] Java 61
N/A Word Search.java Medium [Array, Backtracking, DFS] Java 62
N/A Backpack II.java Medium [Backpack DP, DP] Java 63
N/A Reshape the Matrix.java Easy [] Java 64
N/A Update Bits.java Medium [Bit Manipulation] Java 65
N/A Triangle Count.java Medium [Array] Java 66
N/A Remove Duplicate Letters.java Hard [Greedy, Hash Table, Stack] Java 67
N/A Permutation Sequence.java Medium [Backtracking, Math] Java 68
N/A House Robber II.java Medium [DP, Sequence DP, Status DP] Java 69
N/A O(1) Check Power of 2.java Easy [Bit Manipulation] Java 70
N/A Letter Combinations of a Phone Number.java Medium [Backtracking, String] Java 71
N/A Backspace String Compare.java Easy [Stack, Two Pointers] Java 72
N/A Minimum Size Subarray Sum.java Medium [Array, Binary Search, Subarray, Two Pointers] O(n) O(1) Java 73
N/A Implement Stack using Queues.java Easy [Design, Stack] Java 74
N/A Minimum Absolute Difference in BST.java Easy [BST] Java 75
N/A Maximum Binary Tree.java Medium [Stack, Tree] Java 76
N/A ColorGrid.java Medium [Design, Hash Table] Java 77
N/A HashWithArray.java Easy [] Java 78
N/A Flood Fill.java Easy [DFS] Java 79
N/A Construct Binary Tree from Inorder and Postorder Traversal.java Medium [Array, DFS, Divide and Conquer, Tree] Java 80
N/A Backpack.java Medium [Backpack DP, DP] Java 81
N/A Longest Common Subsequence.java Medium [DP, Double Sequence DP, Sequence DP] Java 82
N/A Peeking Iterator.java Medium [Design] Java 83
N/A Orderly Queue.java Hard [Math, String] Java 84
N/A QuickSort.java Medium [Quick Sort, Sort] Java 85
N/A Maximal Rectangle.java Hard [Array, DP, Hash Table, Stack] Java 86
N/A Expression Evaluation.java Hard [Binary Tree, DFS, Expression Tree, Minimum Binary Tree, Stack] Java 87
N/A Subtree.java Easy [DFS, Tree] Java 88
N/A LFU Cache.java Hard [Design, Hash Table] Java 89
N/A Cosine Similarity.java Easy [Basic Implementation] Java 90
N/A Scramble String.java Hard [DP, Interval DP, String] Java 91
N/A Redundant Connection.java Medium [BFS, DFS, Graph, Tree, Union Find] Java 92
N/A Rotate List.java Medium [Linked List, Two Pointers] Java 93
N/A Swap Nodes in Pairs.java Medium [Linked List] Java 94
N/A Longest Increasing Continuous subsequence.java Easy [Array, Coordinate DP, DP] Java 95
N/A K Edit Distance.java Hard [DP, Double Sequence DP, Sequence DP, Trie] Java 96
N/A Combinations.java Medium [Backtracking, Combination, DFS] Java 97
N/A Max Area of Island.java Easy [Array, DFS] Java 98
N/A Sort List.java Medium [Divide and Conquer, Linked List, Merge Sort, Sort] Java 99
N/A Find Peak Element.java Medium [Array, Binary Search] Java 100
N/A Word Search II.java Hard [Backtracking, DFS, Trie] Java 101
N/A K Empty Slots.java Hard [Array, BST, TreeSet] Java 102
N/A Gray Code.java Medium [Backtracking] Java 103
N/A Encode and Decode TinyURL.java Medium [Hash Table, Math] Java 104
N/A Game of Life.java Medium [Array] Java 105
N/A Compare Version Numbers.java Medium [String] Java 106
N/A Singleton.java Easy [Design] Java 107
N/A Ugly Number.java Medium [Math] Java 108
N/A Russian Doll Envelopes.java Hard [Binary Search, Coordinate DP, DP] Java 109
N/A Rehashing.java Medium [Hash Table] Java 110
N/A Kth Smallest Sum In Two Sorted Arrays.java Hard [] Java 111
N/A Longest Common Substring.java Medium [DP, Double Sequence DP, Sequence DP, String] Java 112
N/A Rotate Image.java Medium [Array, Enumeration] Java 113
N/A Backpack III.java Hard [Backpack DP, DP] Java 114
N/A Combination Sum IV.java Medium [Array, Backpack DP, DP] Java 115
N/A Number of Longest Increasing Subsequence.java Medium [Coordinate DP, DP] O(n^2) Java 116
N/A Permutation Index.java Easy [] Java 117
N/A 4Sum.java Medium [Hash Table] Java 118
N/A Shortest Palindrome.java Hard [KMP, String] Java 119
N/A Convert Sorted Array to Binary Search Tree.java Easy [DFS, Divide and Conquer, Tree] Java 120
N/A Populating Next Right Pointers in Each Node.java Medium [DFS, Divide and Conquer, Tree] Java 121
N/A Space Replacement.java Medium [String] Java 122
N/A Contiguous Array.java Medium [Hash Table] Java 123
N/A Reverse Linked List II .java Medium [Linked List] Java 124
N/A Palindrome Pairs.java Hard [Hash Table, String, Trie] Java 125
N/A Find Peak Element II.java Hard [Binary Search, DFS, Divide and Conquer] Java 126
N/A Minimum Height Trees.java Medium [BFS, Graph] Java 127
N/A Longest Substring Without Repeating Characters.java Medium [Hash Table, String, Two Pointers] Java 128
N/A Fraction to Recurring Decimal.java Medium [Hash Table, Math] Java 129
N/A Wiggle Sort.java Medium [Array, Sort] Java 130
N/A Reverse Words in a String II.java Medium [String] Java 131
N/A Remove Node in Binary Search Tree.java Hard [BST] Java 132
N/A Reorder List.java Medium [Linked List] Java 133
N/A Redundant Connection II.java Hard [DFS, Graph, Tree, Union Find] Java 134
N/A [tool] Quick Select - Median.java Easy [Array, Lint, Quick Select, Quick Sort, Two Pointers] O(n) O(logN) Java 135
N/A Swap Bits.java Easy [Bit Manipulation] Java 136
N/A Friends Of Appropriate Ages.java Medium [Array, Math] Java 137
N/A Longest Increasing Subsequence.java Medium [Binary Search, Coordinate DP, DP, Memoization] O(n^2) dp, O(nLogN) binary search O(n) Java 138
N/A Power of Two.java Easy [Bit Manipulation, Math] Java 139
N/A Min Stack.java Easy [Design, Stack] Java 140
N/A Count of Smaller Number before itself.java Hard [] Java 141
N/A Majority Number III.java Medium [Hash Table, Linked List] Java 142
N/A Number of Digit One.java Hard [Math] Java 143
N/A Tweaked Identical Binary Tree.java Easy [DFS, Tree] Java 144
N/A Search Range in Binary Search Tree .java Medium [BST, Binary Tree] Java 145
N/A Best Time to Buy and Sell Stock III.java Hard [Array, DP, Sequence DP] Java 146
N/A Design Search Autocomplete System.java Hard [Design, Hash Table, MinHeap, PriorityQueue, Trie] input: O(x), where x = possible words, constructor: O(mn) m = max length, n = # of words O(n^2), n = # of possible words, n = # of trie levels; mainlay saving the Map<S, freq> Java 147
N/A Subsets II.java Medium [Array, BFS, Backtracking, DFS] O(2^n) Java 148
N/A One Edit Distance.java Medium [String] Java 149
N/A Segment Tree Modify.java Medium [Binary Tree, DFS, Divide and Conquer, Lint, Segment Tree] Java 150
N/A Distinct Subsequences.java Hard [DP, String] Java 151
N/A Insert Node in a Binary Search Tree .java Easy [BST] Java 152
N/A Container With Most Water.java Medium [Array, Two Pointers] Java 153
N/A Word Ladder.java Medium [BFS] Java 154
N/A Single Number II.java Medium [Bit Manipulation] Java 155
N/A Heaters.java Easy [] Java 156
N/A Kth Smallest Element in a BST.java Medium [BST, DFS, Stack, Tree] Java 157
N/A Robot Room Cleaner.java Hard [Backtracking, DFS] Java 158
N/A Coins in a Line II.java Medium [Array, DP, Game Theory, Memoization, MiniMax] Java 159
N/A Partition List.java Medium [Linked List, Two Pointers] Java 160
N/A Classical Binary Search.java Easy [Binary Search] Java 161
N/A Wood Cut.java Medium [Binary Search] Java 162
N/A Connecting Graph III.java Medium [Union Find] Java 163
N/A Invert Binary Tree.java Easy [BFS, DFS, Tree] Java 164
N/A Remove Duplicates from Unsorted List.java Medium [Linked List] Java 165
N/A Maximum Size Subarray Sum Equals k.java Medium [Hash Table, PreSum, Subarray] O(n) O(n) Java 166
N/A The Smallest Difference.java Medium [Array, Sort, Two Pointers] Java 167
N/A Unique Binary Search Tree II.java Medium [BST, DP, Divide and Conquer, Tree] Java 168
N/A Encode and Decode Strings.java Medium [String] Java 169
N/A Remove Duplicates from Sorted List II.java Medium [Linked List] Java 170
N/A Subarray Sum II.java Hard [Array, Binary Search, Two Pointers] Java 171
N/A Matrix Zigzag Traversal.java Easy [] Java 172
N/A Ones and Zeroes.java Hard [DP] Java 173
N/A Number of Connected Components in an Undirected Graph.java Medium [BFS, DFS, Graph, Union Find] Java 174
N/A Submatrix Sum.java Medium [Array, Hash Table, PreSum] Java 175
N/A Zigzag Iterator.java Medium [BST] Java 176
N/A Find the Connected Component in the Undirected Graph.java Medium [BFS, DFS] Java 177
N/A Implement Stack.java Easy [Stack] Java 178
N/A Number of Airplane in the sky.java Medium [Array, Interval, PriorityQueue, Sort, Sweep Line] Java 179
N/A Surrounded Regions.java Medium [BFS, DFS, Matrix DFS, Union Find] Java 180
N/A Wildcard Matching.java Hard [Backtracking, DP, Double Sequence DP, Greedy, Sequence DP, String] Java 181
N/A Expression Add Operators.java Hard [Backtracking, DFS, Divide and Conquer, String] O(4^n) O(4^n) Java 182
N/A Cracking the Safe.java Hard [DFS, Greedy, Math] Java 183
N/A Unique Word Abbreviation.java Medium [Design, Hash Table] Java 184
N/A Best Time to Buy and Sell Stock IV.java Hard [DP, Sequence DP] Java 185
N/A Find Minimum in Rotated Sorted Array II.java Hard [Array, Binary Search] Java 186
N/A Longest Valid Parentheses.java Hard [Coordinate DP, Stack, String] Java 187
N/A Ugly Number II.java Medium [DP, Enumeration, Heap, Math, PriorityQueue] O(n) O(n) Java 188
N/A Add Two Numbers II.java Medium [Linked List] Java 189
N/A Maximum Average Subarray II.java Review [Array, Binary Search, PreSum] Java 190
N/A Expression Tree Build.java Hard [Binary Tree, Expression Tree, Minimum Binary Tree, Stack] Java 191
N/A Merge Two Binary Trees.java Easy [DFS, Tree] Java 192
N/A Copy Books.java Hard [Binary Search, DP, Partition DP] Java 193
N/A Power of Three.java Easy [Math] Java 194
N/A Sort Colors II.java Medium [Partition, Quick Sort, Sort, Two Pointers] Java 195
N/A Maximum Subarray III.java Review [] Java 196
N/A Path Sum II.java Easy [Backtracking, DFS, Tree] Java 197
N/A Segment Tree Query II.java Medium [Binary Tree, DFS, Divide and Conquer, Lint, Segment Tree] Java 198
N/A Shortest Distance from All Buildings.java Hard [BFS] Java 199
N/A Brick Wall.java Medium [Hash Table] O(mn) O(X), X = max wall width Java 200
N/A Longest Increasing Path in a Matrix.java Hard [Coordinate DP, DFS, DP, Memoization, Topological Sort] Java 201
N/A Interleaving String.java Hard [DP, String] Java 202
N/A Shuffle an Array.java Medium [Permutation] Java 203
N/A Recover Binary Search Tree.java Hard [BST, DFS, Tree] Java 204
N/A My Calendar I.java Medium [Array, TreeMap] Java 205
N/A Evaluate Reverse Polish Notation.java Medium [Stack] O(n) O(n) Java 206
N/A Counting Bits.java Medium [Bit Manipulation, Bitwise DP, DP] Java 207
N/A Sort Letters by Case.java Medium [Partition, Sort, String, Two Pointers] Java 208
N/A Two Strings Are Anagrams.java Easy [] Java 209
N/A Two Sum II - Input array is sorted.java Medium [Array, Binary Search, Two Pointers] Java 210
N/A [HackerRank]. Change to Anagram.java Easy [String] Java 211
N/A Implement Queue using Stacks.java Easy [Design, Stack] Java 212
N/A Basic Calculator.java Hard [Binary Tree, Expression Tree, Math, Minimum Binary Tree, Stack] Java 213
N/A Word Squares.java Hard [Backtracking, Trie] Java 214
N/A Insertion Sort List.java Medium [Linked List, Sort] Java 215
N/A Interval Sum.java Medium [Binary Search, Lint, Segment Tree] Java 216
N/A Strobogrammatic Number II.java Medium [DFS, Enumeration, Math, Sequence DFS] Java 217
N/A The Maze II.java Medium [BFS, DFS, PriorityQueue] Java 218
N/A k Sum.java Hard [DP] Java 219
N/A Coins in a Line III.java Hard [Array, DP, Game Theory, Interval DP, Memoization] Java 220
N/A Convert Sorted List to Binary Search Tree.java Medium [BST, DFS, Divide and Conquer, Linked List] Java 221
N/A Guess Number Higher or Lower.java Easy [Binary Search] Java 222
N/A Trapping Rain Water II.java Hard [BFS, Heap, MinHeap, PriorityQueue] Java 223
N/A Bricks Falling When Hit.java Hard [Union Find] Java 224
N/A Subarray Sum Closest.java Medium [PreSum, PriorityQueue, Sort, Subarray] O(nlogn) O(n) Java 225
N/A Burst Balloons.java Hard [DP, Divide and Conquer, Interval DP, Memoization] Java 226
N/A Partition Array by Odd and Even.java Easy [Array, Two Pointers] Java 227
N/A Best Time to Buy and Sell Stock with Cooldown.java Medium [DP] Java 228
N/A Palindrome Partitioning II.java Hard [DP, Partition DP] Java 229
N/A Convert Binary Search Tree to Sorted Doubly Linked List (extra space).java Medium [Linked List, Stack, Tree] O(n) O(n) Java 230
N/A Kth Largest Element in an Array.java Medium [Divide and Conquer, Heap, MinHeap, PriorityQueue, Quick Sort] Java 231
N/A Sliding Puzzle.java Hard [BFS, Graph] Java 232
N/A Interval Sum II.java Hard [Binary Search, Lint, Segment Tree] Java 233
N/A Add Digits.java Easy [Math] Java 234
N/A HashWithCustomizedClass(LinkedList).java Medium [Hash Table] Java 235
N/A Maximum Vacation Days.java Hard [DP] Java 236
N/A Smallest Subtree with all the Deepest Nodes.java Medium [DFS, Divide and Conquer, Tree] O(n) O(n) Java 237
N/A Kth Smallest Element in a Sorted Matrix.java Medium [Binary Search, Heap] O(n + klogn) O(n) Java 238
N/A Combination Sum III.java Medium [Array, Backtracking, Combination, DFS] Java 239
N/A Last Position of Target.java Easy [Binary Search] Java 240
N/A Path Sum III.java Easy [DFS, Double Recursive, Tree] Java 241
N/A Convert Expression to Reverse Polish Notation.java Hard [Binary Tree, DFS, Expression Tree, Stack] Java 242
N/A Complete Binary Tree.java Easy [BFS, Tree] Java 243
N/A Best Time to Buy and Sell Stock with Transaction Fee.java Medium [Array, DP, Greedy, Sequence DP, Status DP] O(n) O(n), O(1) rolling array Java 244
N/A Pow(x, n).java Medium [Binary Search, Math] Java 245
N/A Maximum Subarray II.java Medium [Array, DP, Greedy, PreSum, Sequence DP, Subarray] Java 246
N/A Sort Colors.java Medium [Array, Partition, Quick Sort, Sort, Two Pointers] Java 247
N/A Word Ladder II.java Hard [Array, BFS, Backtracking, DFS, Hash Table, String] Java 248
N/A Sum of Two Integers.java Easy [Bit Manipulation] Java 249
N/A Predict the Winner.java Medium [DP, MiniMax] Java 250
N/A Connecting Graph II.java Medium [Union Find] Java 251
N/A Search Insert Position.java Easy [] Java 252
N/A Longest Univalue Path.java Easy [] Java 253
N/A Contains Duplicate III.java Medium [BST] Java 254
N/A Spiral Matrix.java Medium [Array, Enumeration] Java 255
N/A Next Closest Time.java Medium [Basic Implementation, Enumeration, String] Java 256
N/A Group Shifted Strings.java Medium [Hash Table, String] Java 257
N/A The Maze III.java Hard [BFS, DFS, PriorityQueue] Java 258
N/A Coins in a Line.java Medium [DP, Game Theory, Greedy] Java 259
N/A Binary Tree Longest Consecutive Sequence.java Medium [DFS, Divide and Conquer, Tree] Java 260
N/A The Spiral Matrix II.java Medium [Array] Java 261
N/A Trim a Binary Search Tree.java Easy [BST, Tree] Java 262
N/A Number Of Corner Rectangles.java Medium [DP, Math] Java 263
N/A Queue Reconstruction by Height.java Medium [Greedy] Java 264
N/A Minimum Swaps To Make Sequences Increasing.java Medium [Coordinate DP, DP, Status DP] Java 265
N/A Interleaving Positive and Negative Numbers.java Medium [Two Pointers] Java 266
N/A Path Sum IV.java Medium [DFS, Hash Table, Tree] Java 267
N/A Excel Sheet Column Number.java Easy [Math] Java 268
N/A Target Sum.java Medium [DFS, DP] Java 269
N/A Partition Array.java Medium [Array, Quick Sort, Sort, Two Pointers] Java 270
N/A Bus Routes.java Hard [BFS] Java 271
N/A Max Sum of Rectangle No Larger Than K.java Hard [Array, BST, Binary Search, DP, Queue, TreeSet] Java 272
N/A String Permutation.java Easy [] Java 273
N/A Maximum XOR of Two Numbers in an Array.java Medium [Bit Manipulation, Trie] Java 274
N/A Search for a Range.java Medium [Array, Binary Search] Java 275
N/A Palindrome Permutation II.java Medium [Backtracking, Permutation] Java 276
N/A Populating Next Right Pointers in Each Node II.java Medium [DFS, Tree] O(n) O(1) Java 277
N/A Nim Game.java Easy [Brainteaser, DP, Game Theory] Java 278
N/A Search a 2D Matrix.java Medium [Array, Binary Search] Java 279
N/A Largest Rectangle in Histogram.java Hard [Array, Monotonous Stack, Stack] Java 280
[lint] [lint]. Merge k Sorted Arrays.java Medium [Heap, MinHeap, PriorityQueue] O(nlogk) O(k) Java 281
[lint] [lint]. Segment Tree Build II.java Medium [Binary Tree, Divide and Conquer, Lint, Segment Tree] Java 282
[lint] [lint]. Nth to Last Node in List.java Easy [Linked List, Lint] Java 283
[lint] [lint]. Product of Array Exclude Itself.java Medium [Array, Lint] Java 284
[lint] [lint]. Compare Strings.java Easy [Lint, String] Java 285
[lint] [lint]. Segment Tree Query.java Medium [Binary Tree, DFS, Divide and Conquer, Lint, Segment Tree] Java 286
[lint] [lint]. HashHeap.java Hard [HashHeap, Heap, Lint] Java 287
[lint] [lint]. Longest Words.java Easy [Hash Table, Lint, String] Java 288
[lint] [lint]. Anagrams.java Medium [Array, Hash Table, Lint] O(n) O(n) Java 289
[lint] [lint]. 3 Sum Closest.java Medium [Array, Lint, Two Pointers] Java 290
[lint] [lint]. Unique Characters.java Easy [Array, Lint, String] Java 291
[lint] [lint]. Lowest Common Ancestor II.java Easy [Hash Table, Lint, Tree] Java 292
[lint] [lint]. Heapify.java Medium [HashHeap, Heap, Lint, MinHeap] Java 293
[lint] [lint]. Subarray Sum.java Easy [Array, Hash Table, Lint, PreSum, Subarray] O(n) O(n) Java 294
[lint] [lint]. Recover Rotated Sorted Array.java Easy [Array, Lint] Java 295
[lint] [lint]. 2 Sum II.java Medium [Array, Binary Search, Lint, Two Pointers] Java 296
[lint] [lint]. Segment Tree Build.java Medium [Binary Tree, Divide and Conquer, Lint, Segment Tree] Java 297
[tool] [tool]. MergeSort.java Medium [Lint, Merge Sort, Sort] O(mlogn) O(n) Java 298
[tool] [tool]. Hash Function.java Easy [Hash Table, Lint] O(1) get O(n) store map Java 299
[tool] [tool]. UnionFind.java Medium [Lint, Union Find] O(n), with Path Compression O(mN), with Union by Rank O(logN) O(n) Java 300
[tool] [tool]. Topological Sorting.java Medium [BFS, DFS, Lint, Topological Sort] O(V + E) O(V + E) Java 301
36 36. Valid Sudoku.java Easy [Enumeration, Hash Table] (mn) (mn) Java 302
359 359. Logger Rate Limiter.java Easy [Design, Hash Table] O(1) O(n) Java 303
198 198. House Robber.java Easy [DP, Sequence DP, Status DP] O(n) O(n) or rolling array O(1) Java 304
21 21. Merge Two Sorted Lists.java Easy [Linked List] O(n) O(1) Java 305
102 102. Binary Tree Level Order Traversal.java Medium [BFS, DFS, Tree] O(n) O(n) Java 306
788 788. Rotated Digits.java Easy [Basic Implementation, String] O(n) O(n) Java 307
42 42. Trapping Rain Water.java Hard [Array, Stack, Two Pointers] O(n) O(1) Java 308
347 347. Top K Frequent Elements.java Medium [Hash Table, Heap, MaxHeap, MinHeap, PriorityQueue] O(n) O(n) Java 309
269 269. Alien Dictionary.java Hard [BFS, Backtracking, DFS, Graph, Topological Sort] O(n), n = # of graph edges O(n) Java 310
237 237. Delete Node in a Linked List.java Easy [Linked List] Java 311
142 142. Linked List Cycle II.java Medium [Cycle Detection, Linked List, Slow Fast Pointer, Two Pointers] O(n) O(1) Java 312
448 448. Find All Numbers Disappeared in an Array.java Easy [Array, Bucket Sort] O(n) O(1) Java 313
360 360. Sort Transformed Array.java Medium [Math, Two Pointers] O(n) O(n) store result Java 314
22 22. Generate Parentheses.java Medium [Backtracking, DFS, Sequence DFS, String] O(2^n) O(2^n) Java 315
849 849. Maximize Distance to Closest Person.java Easy [Array, Basic Implementation, Two Pointers] O(n) O(1) Java 316
408 408. Valid Word Abbreviation.java Easy [Basic Implementation, String] Java 317
415 415. Add Strings.java Easy [Basic Implementation, Math, String] O(n) O(n) Java 318
83 83. Remove Duplicates from Sorted List.java Easy [Linked List] Java 319
1108 1108. Defanging an IP Address.java Easy [Basic Implementation, String] Java 320
1021 1021. Remove Outermost Parentheses.java Easy [Stack] Java 321
236 236. Lowest Common Ancestor of a Binary Tree.java Medium [DFS, Tree] O(n) O(n) Java 322
766 766. Toeplitz Matrix.java Easy [Array] O(mn) O(1) Java 323
953 953. Verifying an Alien Dictionary.java Easy [Hash Table] O(nm) O(1) Java 324
1053 1053. Previous Permutation With One Swap.java Medium [Array, Greedy, Permutation] O(n) O(1) Java 325
1213 1213. Intersection of Three Sorted Arrays.java Easy [Hash Table, Two Pointers] O(m + n + h) two pointers approach O(1) Java 326
383 383. Ransom Note.java Easy [Basic Implementation, String] Java 327
56 56. Merge Intervals.java Medium [Array, PriorityQueue, Sort, Sweep Line] O(nlogn) O(n) Java 328
252 252. Meeting Rooms.java Easy [PriorityQueue, Sort, Sweep Line] O(nlogn) O(1) Java 329
665 665. Non-decreasing Array.java Easy [Array] O(n) O(1) Java 330
843 843. Guess the Word.java Hard [MiniMax] TODO TODO Java 331
986 986. Interval List Intersections.java Medium [Two Pointers] O(n) O(1) Java 332
76 76. Minimum Window Substring.java Hard [Hash Table, Sliding Window, String, Two Pointers] O(n) O(1) Java 333
293 293. Flip Game.java Easy [String] Java 334
244 244. Shortest Word Distance II.java Medium [Array, Design, Hash Table, Two Pointers] O(n) to build map, O(a + b) to query O(n) Java 335
686 686. Repeated String Match.java Easy [Basic Implementation, Edge Case, String] Java 336
80 80.Remove Duplicates from Sorted Array II.java Medium [Array, Two Pointers] Java 337
301 301. Remove Invalid Parentheses.java Hard [BFS, DFS, DP] Java 338
111 111. Minimum Depth of Binary Tree.java Easy [BFS, DFS, Tree] O(n) O(n) Java 339
1216 1216. Valid Palindrome III.java Hard [DFS, DP, Memoization, String] O(n^2) O(n^2) Java 340
7 7. Reverse Integer.java Easy [Math] O(n) O(1) Java 341
5 5. Longest Palindromic Substring.java Medium [DP, String] O(n^2) O(n^2) Java 342
303 303. Range Sum Query - Immutable.java Easy [DP, PreSum] O(1) query, O(n) setup O(n) Java 343
674 674. Longest Continuous Increasing Subsequence.java Easy [Array, Coordinate DP, DP, Sliding Window] O(n) O(1) Java 344
1007 1007. Minimum Domino Rotations For Equal Row.java Medium [Array, Greedy] O(n) O(1) Java 345
485 485. Max Consecutive Ones.java Easy [Array, Basic Implementation] O(n) O(1) Java 346
896 896. Monotonic Array.java Easy [Array] Java 347
207 207. Course Schedule.java Medium [BFS, Backtracking, DFS, Graph, Topological Sort] O(n) O(n) Java 348
327 327. Count of Range Sum.java Hard [BIT, Divide and Conquer, Merge Sort, PreSum, Segment Tree] O(nlogn) O(n) Java 349
987 987. Vertical Order Traversal of a Binary Tree.java Medium [BFS, Binary Tree, DFS, Hash Table, Tree] Java 350
26 26.Remove Duplicates from Sorted Array.java Easy [Array, Two Pointers] Java 351
429 429. N-ary Tree Level Order Traversal.java Medium [BFS, Tree] O(n) O(n) Java 352
275 275. H-Index II.java Medium [Binary Search] O(logN) O(1) extra Java 353
204 204. Count Primes.java Easy [Hash Table, Math] Java 354
58 58. Length of Last Word.java Easy [String] Java 355
496 496. Next Greater Element I.java Easy [Hash Table, Stack] O(n) O(n) Java 356
41 41. First Missing Positive.java Hard [Analysis, Array, Edge Case] O(n) O(1) Java 357
694 694. Number of Distinct Islands.java Medium [DFS, Hash Table] O(n) O(n) Java 358
717 717. 1-bit and 2-bit Characters.java Easy [Array] Java 359
53 53. Maximum Subarray.java Easy [Array, DFS, DP, Divide and Conquer, PreSum, Sequence DP, Subarray] O(n) O(n), O(1) rolling array Java 360
152 152. Maximum Product Subarray.java Medium [Array, DP, PreProduct, Subarray] O(n) O(1) Java 361
199 199. Binary Tree Right Side View.java Medium [BFS, DFS, Tree] O(n) O(n) Java 362
259 259. 3Sum Smaller.java Medium [Array, Sort, Two Pointers] Java 363
977 977. Squares of a Sorted Array.java Easy [Array, Two Pointers] O(n) O(n) Java 364
824 824. Goat Latin.java Easy [Basic Implementation, String] O(n) O(1) Java 365
308 308. Range Sum Query 2D - Mutable.java Hard [Binary Indexed Tree, Segment Tree] build(n), update(logn), rangeRuery(logn + k) O(n) Java 366
1203 1203. Sort Items by Groups Respecting Dependencies.java Hard [BFS, DFS, Graph, Topological Sort] O(V + E) to traverse the graph, #nodes + #edges O(V + E) Java 367
1153 1153. String Transforms Into Another String.java Hard [Graph] O(n) O(n) Java 368
1008 1008. Construct Binary Search Tree from Preorder Traversal.java Medium [DFS, Tree] O(n) O(n) Java 369
151 151. Reverse Words in a String.java Medium [String] O(n) Java 370
855 855. Exam Room.java Medium [PriorityQueue, Sort, TreeMap, TreeSet] O(logn) O(n) Java 371
31 31. Next Permutation.java Medium [Array, Permutation] O(n) O(1) Java 372
518 518. Coin Change 2.java Medium [Backpack DP, DP] O(n) O(n) Java 373
405 405. Convert a Number to Hexadecimal.java Easy [Bit Manipulation] Java 374
850 850. Rectangle Area II.java Hard [Segment Tree, Sweep Line] O(n^2) O(n) Java 375
515 515. Find Largest Value in Each Tree Row.java Medium [BFS, DFS, Tree] O(n) O(n) Java 376
253 253. Meeting Rooms II.java Medium [Greedy, Heap, PriorityQueue, Sort, Sweep Line] O(nlogn) O(n) Java 377
1161 1161. Maximum Level Sum of a Binary Tree.java Medium [BFS, DFS, Graph] O(n) visit all nodes O(n) Java 378
509 509. Fibonacci Number.java Easy [DP, Math, Memoization] Java 379
221 221. Maximal Square.java Medium [Coordinate DP, DP] O(mn) O(mn) Java 380
131 131. Palindrome Partitioning.java Medium [Backtracking, DFS] O(2^n) O(n^2) Java 381
136 136. Single Number.java Easy [Bit Manipulation, Hash Table] Java 382
222 222. Count Complete Tree Nodes.java Medium [Binary Search, DFS, Tree] O(n) O(h) Java 383
257 257. Binary Tree Paths.java Easy [Backtracking, Binary Tree, DFS] O(n) O(nlogn) Java 384
543 543. Diameter of Binary Tree.java Easy [Tree] O(n) when non-balanced O(n) when non-balanced Java 385
398 398. Random Pick Index.java Medium [Reservior Sampling] O(n) O(n) for input int[], O(1) extra space used Java 386
238 238. Product of Array Except Self.java Medium [Array, PreProduct] O(n) O(1) Java 387
1060 1060. Missing Element in Sorted Array.java Medium [Binary Search] O(logn) O(1) Java 388
1048 1048. Longest String Chain.java Medium [Bucket Sort, DP, Hash Table, Sort] O(n) O(n) Java 389
67 67. Add Binary.java Easy [Math, String, Two Pointers] Java 390
299 299. Bulls and Cows.java Medium [Hash Table] O(n) O(n) Java 391
557 557. Reverse Words in a String III.java Easy [String] Java 392
203 203. Remove Linked List Elements.java Easy [Linked List] Java 393
1219 1219. Path with Maximum Gold.java Medium [Backtracking, DFS] O(n^2) O(n) recursive depth Java 394
266 266. Palindrome Permutation.java Easy [Hash Table] O(n) O(n) Java 395
62 62. Unique Path.java Medium [Array, Coordinate DP, DP] O(mn) O(mn), rolling array O(n) Java 396
1091 1091. Shortest Path in Binary Matrix.java Medium [BFS] O(n^2) Java 397
1110 1110. Delete Nodes And Return Forest.java Medium [DFS, Divide and Conquer, Tree] O(n) O(logn) Java 398
1249 1249. Minimum Remove to Make Valid Parentheses.java Medium [Stack, String] O(n) O(n) Java 399
15 15. 3Sum.java Medium [Array, Sort, Two Pointers] O(n^2) Java 400
311 311. Sparse Matrix Multiplication.java Medium [Hash Table] O(mnk), where m = A.row, n = B.col, k = A.col = B.row O(1) extra Java 401
339 339. Nested List Weight Sum.java Easy [BFS, DFS, NestedInteger] O(n) O(h), h = levels Java 402
322 322. Coin Change.java Medium [Backpack DP, DFS, DP, Memoization] O(n * S) O(S) Java 403
55 55. Jump Game.java Medium [Array, DP, Greedy] O(n) O(1) Java 404
173 173. Binary Search Tree Iterator.java Medium [BST, Design, Stack, Tree] O(1) average O(h) Java 405
140 140. Word Break II.java Hard [Backtracking, DFS, DP, Hash Table, Memoization] O(n!) O(n!) Java 406
51 51. N-Queens.java Hard [Backtracking] O(n!) O(n^2) Java 407
875 875. Koko Eating Bananas.java Medium [Binary Search] O(n*logM) O(1) Java 408
189 189. Rotate Array.java Easy [Array, Rotation] Java 409
19 19. Remove Nth Node From End of List.java Medium [Linked List, Two Pointers] O(n) O(1) Java 410
134 134. Gas Station.java Medium [Greedy] O(n) O(1) Java 411
119 119. Pascal's Triangle II.java Easy [Array, Basic Implementation] O(k^2), pascal triangle size O(k^2) Java 412
1197 1197. Minimum Knight Moves.java Medium [BFS] O(8^n) O(8^n) Java 413
493 493. Reverse Pairs.java Medium [BST, Binary Indexed Tree, Divide and Conquer, Merge Sort, Segment Tree] Java 414
1306 1306. Jump Game III.java Medium [BFS, Graph] O(n) O(n) Java 415
305 305. Number of Islands II.java Hard [Union Find] O(k * log(mn)) O(mn) Java 416
206 206. Reverse Linked List.java Easy [Linked List] Java 417
277 277. Find the Celebrity.java Medium [Adjacency Matrix, Array, Graph, Greedy, Pruning] O(n) O(1) Java 418
741 741. Cherry Pickup.java Hard [DFS, DP] O(n^3) O(n^3), memo size Java 419
168 168. Excel Sheet Column Title.java Easy [Math] O(n) O(1) Java 420
104 104. Maximum Depth of Binary Tree.java Easy [DFS, Tree] Java 421
349 349. Intersection of Two Arrays.java Easy [Binary Search, Hash Table, Sort, Two Pointers] O(m + n) O(m + n) Java 422
443 443. String Compression.java Easy [Basic Implementation, String] Java 423
297 297. Serialize and Deserialize Binary Tree.java Hard [BFS, DFS, Deque, Design, Divide and Conquer, Tree] O(n) O(n) Java 424
46 46. Permutations.java Medium [BFS, Backtracking, DFS, Permutation] O(n!) O(n!) Java 425
844 844. Backspace String Compare.java Easy [Stack, Two Pointers] O(n) O(1) Java 426
9 9. Palindrome Number.java Easy [Math] Java 427
1094 1094. Car Pooling.java Medium [Greedy, Heap, PriorityQueue, Sort] O(n) O(1) only use bucket size 1000 Java 428
245 245. Shortest Word Distance III.java Medium [Array, Design, Hash Table, Two Pointers] O(n) O(1) Java 429
1117 1117. Building H2O.java Medium [Lock, Semaphore, Thread] Java 430
973 973. K Closest Points to Origin.java Medium [Divide and Conquer, Heap, Sort] O(klogk) O(k) Java 431
771 771. Jewels and Stones.java Easy [Hash Table] O(n) O(n) Java 432
200 200. Number of Islands.java Medium [BFS, DFS, Matrix DFS, Union Find] O(n) O(n) Java 433
141 141. Linked List Cycle.java Easy [Cycle Detection, Linked List, Slow Fast Pointer, Two Pointers] O(n) O(1) Java 434
567 567. Permutation in String.java Medium [Sliding Window, Two Pointers] O(m + n) O(1) Java 435
727 727. Minimum Window Subsequence.java Hard [DP, Hash Table, Sliding Window, String, Two Pointers] O(n^2) O(1) Java 436
158 158. Read N Characters Given Read4 II - Call multiple times.java Hard [Enumeration, String] O(n) O(n) Java 437
369 369. Plus One Linked List.java Medium [Linked List] O(n) O(1) Java 438
211 211. Add and Search Word - Data structure design.java Medium [Backtracking, Design, Trie] O(n) to search and to add word < O(mn), depends on the input. m = # of words Java 439
43 43. Multiply Strings.java Medium [Math, String] O(mn) O(mn) Java 440
621 621. Task Scheduler.java Medium [Array, Enumeration, Greedy, PriorityQueue, Queue] O(n) O(1) Java 441
680 680. Valid Palindrome II.java Easy [String] Java 442
295 295. Find Median from Data Stream.java Hard [Design, Heap, MaxHeap, MinHeap] O(1) get, O(logn) addNum O(n) Java 443
70 70. Climbing Stairs.java Easy [DP, Memoization, Sequence DP] Java 444
747 747. Largest Number At Least Twice of Others.java Easy [Array] Java 445
315 315. Count of Smaller Numbers After Self.java Hard [BST, Binary Indexed Tree, Binary Search, Divide and Conquer, Segment Tree] O(nlogn) O(n) Java 446
239 239. Sliding Window Maximum.java Hard [Deque, Heap, Sliding Window] O(n) O(n) Java 447
47 47. Permutations II.java Medium [Backtracking, DFS] Java 448
332 332. Reconstruct Itinerary.java Medium [Backtracking, DFS, Graph] O(n^n) O(�m) Java 449
88 88. Search in Rotated Sorted Array II.java Medium [Array, Binary Search] O(logn), worst O(n) O(1) Java 450
561 561. Array Partition I.java Easy [Array] O(nlogn) O(1) Java 451
387 387. First Unique Character in a String.java Easy [Hash Table, String] O(n) O(256) = O(1) Java 452
345 345. Reverse Vowels of a String.java Easy [String, Two Pointers] Java 453
39 39. Combination Sum.java Medium [Array, Backtracking, Combination, DFS] O(k * 2^n), k = avg rst length O(k) stack depth, if not counting result size Java 454
10 10. Regular Expression Matching.java Hard [Backtracking, DP, Double Sequence DP, Sequence DP, String] Java 455
367 367. Valid Perfect Square.java Easy [Binary Search, Math] O(logN) O(1) Java 456
270 270. Closest Binary Search Tree Value.java Easy [BST, Binary Search, Tree] O(logn) O(1) Java 457
28 28. Implement strStr().java Easy [String, Two Pointers] Java 458
1106 1106. Parsing A Boolean Expression.java Hard [DFS, Stack, String] Java 459
144 144. Binary Tree Preorder Traversal.java Medium [BFS, DFS, Stack, Tree] O(n) O(n) Java 460
852 852. Peak Index in a Mountain Array.java Easy [Binary Search] O(logn) O(1) Java 461
146 146. LRU Cache.java Medium [Design, Doubly Linked List, Hash Table, Linked List] O(1) O(1) Java 462
110 110. Balanced Binary Tree.java Easy [DFS, Tree] Java 463
1040 1040. Moving Stones Until Consecutive II.java Medium [Array, Sliding Window] O(nlogn) O(n) Java 464
246 246. Strobogrammatic Number.java Easy [Enumeration, Hash Table, Math, Two Pointers] O(n) O(1) Java 465
100 100. Same Tree.java Easy [BFS, DFS, Tree] O(n) O(logn) Java 466
307 307. Range Sum Query - Mutable.java Medium [Binary Indexed Tree, Segment Tree] build O(n), query (logn +k), update O(logn) O(n) Java 467
88 88. Merge Sorted Array.java Easy [Array, Two Pointers] O(n) O(1) Java 468
319 319. Bulb Switcher.java Medium [Brainteaser, Math] O(1) O(1) Java 469
112 112. Path Sum.java Easy [DFS, Tree] Java 470
463 463. Island Perimeter.java Easy [Hash Table] O(n) Java 471
170 170. Two Sum III - Data structure design.java Easy [Design, Hash Table, Memoization] O(n) O(n) Java 472
122 122. Best Time to Buy and Sell Stock II.java Easy [Array, DP, Greedy, Sequence DP, Status DP] O(n) O(1) greedy, O(n) dp Java 473
715 715. Range Module.java Hard [Segment Tree, TreeSet] query O(logn), update O(n) O(n) Java 474
12 12. Integer to Roman.java Medium [Basic Implementation, Math, String] O(n) O(n) Java 475
14 14. Longest Common Prefix.java Easy [String] Java 476
243 243. Shortest Word Distance.java Easy [Array, Two Pointers] O(n) O(1) Java 477
414 414. Third Maximum Number.java Easy [Array, PriorityQueue] Java 478
1267 1267. Count Servers that Communicate.java Medium [Array, Graph] O(mn) O(m + n) Java 479
20 20. Valid Parentheses.java Easy [Stack, String] O(n) O(n) Java 480
893 893. Groups of Special-Equivalent Strings.java Easy [Basic Implementation, String] Java 481
427 427. Construct Quad Tree.java Medium [Tree] O(n^2) O(n^2) Java 482
981 981. Time Based Key-Value Store.java Medium [Binary Search, Hash Table, TreeMap] set O(1), get(logn) O(n) Java 483
169 169. Majority Element.java Easy [Array, Bit Manipulation, Divide and Conquer, Moore Voting, Sort] O(n) O(1) Java 484
234 234. Palindrome Linked List.java Easy [Linked List, Two Pointers] O(n) O(1) Java 485
202 202. Happy Number.java Easy [Hash Table, Math] O(m), m iterations O(m), m number in set Java 486
69 69. Sqrt(x).java Easy [Binary Search, Math] Java 487
876 876. Middle of Linked List.java Easy [Linked List] Java 488
1026 1026. Maximum Difference Between Node and Ancestor.java Medium [DFS, Tree] O(n) O(logn) Java 489
78 78. Subsets.java Medium [Array, BFS, Backtracking, Bit Manipulation, DFS] O(2^n) O(2^n) Java 490
432 432. All One Data Structure.java Hard [Design, Doubly Linked List] O(1) O(n) Java 491
380 380. Insert Delete GetRandom O(1).java Medium [Array, Design, Hash Table] O(1) avg O(n) Java 492
560 560. Subarray Sum Equals K.java Medium [Array, Hash Table, PreSum, Subarray] O(n) O(n) Java 493
219 219. Contains Duplicate II.java Easy [Array, Hash Table] O(n) O(n) Java 494
91 91. Decode Ways.java Medium [DP, Partition DP, String] O(n) O(n) Java 495
205 205. Isomorphic Strings.java Easy [Hash Table] O(n) O(n) Java 496
639 639. Decode Ways II.java Hard [DP, Enumeration, Partition DP] O(n) O(n) Java 497
346 346. Moving Average from Data Stream.java Easy [Design, Queue, Sliding Window] O(1) for next() O(size) for fixed storage Java 498
145 145. Binary Tree Postorder Traversal.java Medium [Stack, Tree, Two Stacks] O(n) O(n) Java 499
938 938. Range Sum of BST.java Easy [BST, Recursion, Tree] Java 500
210 210. Course Schedule II.java Medium [BFS, DFS, Graph, Topological Sort] O(n) O(n) Java 501
68 68. Text Justification.java Hard [Enumeration, String] O(n) go over words O(maxLength) buffer list Java 502
314 314. Binary Tree Vertical Order Traversal.java Medium [BFS, DFS, Hash Table, Tree] O(n) O(n) Java 503
287 287. Find the Duplicate Number.java Medium [Array, Binary Search, Binary Search on Value, Cycle Detection, Slow Fast Pointer, Two Pointers] O(n) O(1) Java 504
242 242. Valid Anagram.java Easy [Hash Table, Sort] O(n) O(1), unique chars Java 505
340 340. Longest Substring with At Most K Distinct Characters.java Hard [Hash Table, LinkedHashMap, Sliding Window, String, Two Pointers] O(n) O(k) Java 506
217 217. Contains Duplicate.java Easy [Array, Hash Table] O(n) O(1) Java 507
103 103. Binary Tree Zigzag Level Order Traversal.java Medium [BFS, Stack, Tree] O(n) O(n) Java 508
1057 1057. Campus Bikes.java Medium [Bucket Sort, Greedy, PriorityQueue, Sort] O(mn) O(mn) Java 509
261 261. Graph Valid Tree.java Medium [BFS, DFS, Graph, Union Find] Java 510
64 64. Minimum Path Sum.java Medium [Array, Coordinate DP, DP] O(mn) O(n) rolling array Java 511
796 796. Rotate String.java Easy [String] Java 512
229 229. Majority Element II.java Medium [Array, Moore Voting] O(n) (1) Java 513
1041 1041. Robot Bounded In Circle.java Easy [String] Java 514
2 2. Add Two Numbers.java Medium [Linked List, Math] O(max(m,n)) O(max(m,n)) Java 515
157 157. Read N Characters Given Read4.java Easy [Enumeration, String] Java 516
114 114. Flatten Binary Tree to Linked List.java Medium [Binary Tree, DFS] O(n) O(n), stacks Java 517
121 121. Best Time to Buy and Sell Stock.java Easy [Array, DP, Sequence DP] Java 518
1004 1004. Max Consecutive Ones III.java Medium [Sliding Window, Two Pointers] O(n) O(1) Java 519
1146 1146. Snapshot Array.java Medium [Array, Hash Table, TreeMap] O(1) set, O(logn) get, O(x) snap, x = # of changes O(n * m), n = array size, m = # of snaps Java 520
273 273. Integer to English Words.java Hard [Enumeration, Math, String] O(n) O(1) Java 521
304 304. Range Sum Query 2D - Immutable.java Medium [DP, PreSum] O(mn) build, O(1) query O(mn) Java 522
605 605. Can Place Flowers.java Easy [Array, Greedy] O(n) O(1) Java 523
1 1. Two Sum.java Easy [Array, Hash Table] O(n) O(n) Java 524
118 118. Pascal's Triangle.java Easy [Array, Basic Implementation, List] O(n^2) based on pascal triangle size O(n^2) Java 525
23 23. Merge k Sorted Lists.java Medium [Divide and Conquer, Heap, Linked List, Merge Sort, PriorityQueue] O(nlogk) O(logk) Java 526
283 283. Move Zeroes.java Easy [Array, Two Pointers] O(n) O(1) Java 527
208 208. Implement Trie (Prefix Tree).java Medium [Design, Trie] Java 528
516 516. Longest Palindromic Subsequence.java Medium [DFS, DP, Interval DP, Memoization] O(n^2) O(n^2) Java 529
218 218. The Skyline Problem.java Hard [BIT, Divide and Conquer, HashHeap, Heap, PriorityQueue, Segment Tree, Sweep Line] O(n^2logn) O(n) Java 530
430 430. Flatten a Multilevel Doubly Linked List.java Medium [DFS, Linked List] O(n) O(1) Java 531
63 63. Unique Paths II.java Medium [Array, Coordinate DP, DP] O(mn) O(mn) Java 532
52 52. N-Queens II.java Hard [Backtracking] O(n!) O(n) Java 533
1033 1033. Moving Stones Until Consecutive.java Easy [Basic Implementation, Sort] O(1), only 3 elements O(1) Java 534
139 139. Word Break.java Medium [DP, Hash Table, Sequence DP] O(n^2) O(n) Java 535
105 105. Construct Binary Tree from Preorder and Inorder Traversal.java Medium [Array, DFS, Divide and Conquer, Hash Table, Tree] O(n) O(n) Java 536
125 125. Valid Palindrome.java Easy [String, Two Pointers] Java 537
449 449. Serialize and Deserialize BST.java Medium [Tree] O(n) O(��n) Java 538
274 274.H-Index.java Medium [Bucket Sort, Hash Table, Sort] O(n) O(n) Java 539
160 160. Intersection of Two Linked Lists.java Easy [Linked List] Java 540
40 40. Combination Sum II.java Medium [Array, Backtracking, Combination, DFS] O(k * 2^n), k = avg rst length O(n) stack depth, if not counting result size Java 541
410 410. Split Array Largest Sum.java N/A [] Java 542
724 724. Find Pivot Index.java Easy [Array, PreSum] O(n) O(1) Java 543
523 523. Continuous Subarray Sum.java Medium [Coordinate DP, DP, Math, PreSum, Subarray] O(n) O(k) Java 544
65 65. Valid Number.java Hard [Enumeration, Math, String] O(n) O(1) Java 545
350 350. Intersection of Two Arrays II.java Easy [Binary Search, Hash Table, Sort, Two Pointers] (n) (n) Java 546
364 364. Nested List Weight Sum II.java Medium [DFS, NestedInteger] O(n), visit all nodes O(h), depth Java 547
49 49. Group Anagrams.java Medium [Hash Table, String] O(nk) O(nk) Java 548
720 720. Longest Word in Dictionary.java Easy [Hash Table, Trie] O(nlogn) O(n) Java 549
438 438. Find All Anagrams in a String.java Medium [Hash Table, Sliding Window, Two Pointers] O(n) O(1) Java 550
632 632. Smallest Range Covering Elements from K Lists.java Hard [Hash Table, Sliding Window, Two Pointers] O(nlogn), n = total elements O(n) to store sorted list Java 551
138 138. Copy List with Random Pointer.java Medium [Hash Table, Linked List] O(n) O(n) Java 552
159 159. Longest Substring with At Most Two Distinct Characters.java Medium [Hash Table, Sliding Window, String, Two Pointers] O(n) O(1) Java 553
1043 1043. Partition Array for Maximum Sum.java Medium [DFS, DP, Graph, Memoization] O(n), calc memo[n] O(n) Java 554
33 33. Search in Rotated Sorted Array.java Medium [Array, Binary Search] O(logn) O(1) Java 555
760 760. Find Anagram Mappings.java Easy [Hash Table] O(n) O(n) Java 556
133 133. Clone Graph.java Medium [BFS, DFS, Graph] O(n) O(n) Java 557
743 743. Network Delay Time.java Medium [BFS, DFS, Graph, Heap, PQ] O(nlogn) O(n) Java 558
636 636. Exclusive Time of Functions.java Medium [Stack] O(n) O(n) Java 559
692 692. Top K Frequent Words.java Medium [Hash Table, Heap, MaxHeap, MinHeap, PriorityQueue, Trie] O(n) O(n) Java 560
1170 1170. Compare Strings by Frequency of the Smallest Character.java Easy [Array, String] O(m + n) O(m + n) Java 561
426 426. Convert Binary Search Tree to Sorted Doubly Linked List.java Medium [BST, DFS, Divide and Conquer, Linked List, Tree] O(n) O(1) Java 562
745 745. Prefix and Suffix Search.java Hard [Trie] O(N + Q) O(N) Java 563
8 8. String to Integer (atoi).java Medium [Math, String] O(n) O(n) Java 564
361 361. Bomb Enemy.java Medium [Coordinate DP, DP] O(mn) O(n) by calculating column sum Java 565
94 94. Binary Tree Inorder Traversal.java Easy [Hash Table, Stack, Tree] O(n) O(logn) Java 566
402 402. Remove K Digits.java Medium [Greedy, Monotonous Stack, Stack] O(n) O(n) Java 567
98 98. Validate Binary Search Tree.java Medium [BST, DFS, Divide and Conquer, Tree] O(n) O(logn) Java 568
1123 1123. Lowest Common Ancestor of Deepest Leaves.java Medium [BFS, DFS, Tree] O(n) O(n) Java 569
921 921. Minimum Add to Make Parentheses Valid.java Medium [] O(n) O(1) Java 570
399 399. Evaluate Division.java Medium [BFS, DFS, Graph, Union Find] Java 571
785 785. Is Graph Bipartite.java Medium [BFS, DFS, Garph] O(n) O(n) Java 572
767 767. Reorganize String.java Medium [Greedy, Hash Table, Heap, Sort, String] O(m), m = # of unique letters O(nLogm), n = length Java 573
71 71. Simplify Path.java Medium [Stack, String] O(n) O(n) Java 574
34 34. Find First and Last Position of Element in Sorted Array.java Medium [Array, Binary Search] O(logn) O(1) Java 575
278 278. First Bad Version.java Easy [Binary Search] O(logN) O(1) Java 576
124 124. Binary Tree Maximum Path Sum.java Hard [DFS, DP, Tree, Tree DP] O(n) O(logn) Java 577
721 721. Accounts Merge.java Medium [DFS, Hash Table, Union Find] Java 578
689 689. Maximum Sum of 3 Non-Overlapping Subarrays.java Hard [Array, DP] O(n) O(n) Java 579
101 101. Symmetric Tree.java Easy [BFS, DFS, Tree] O(n) O(n) Java 580
149 149. Max Points on a Line.java Hard [Array, Geometry, Hash Table, Math] O(n^2) O() Java 581
698 698. Partition to K Equal Sum Subsets.java Medium [DFS, DP, Recursion] O(k^(n-k) * k!) O(n) Java 582
57 57. Insert Interval.java Hard [Array, PriorityQueue, Sort, Sweep Line] O(n) O(n) Java 583
13 13. Roman to Integer.java Easy [Math, String] O(n) O(1) Java 584
716 716. Max Stack.java Medium [Design, Doubly Linked List, Stack, TreeMap] avg O(1), [O(logN) peekMax(), TreeMap]; [O(n) popMax(), TwoStack] O(n) Java 585
671 671. Second Minimum Node In a Binary Tree.java Easy [BFS, Tree] O(n) O(n) leaf nodes Java 586
366 366. Find Leaves of Binary Tree.java Medium [DFS, Tree] O(n) O(h) Java 587
235 235. Lowest Common Ancestor of a Binary Search Tree.java Easy [BST, DFS, Tree] O(logn) O(logn) Java 588
156 156. Binary Tree Upside Down.java Medium [DFS, Tree] O(n) O(h) Java 589
416 416. Partition Equal Subset Sum.java Medium [Backpack, DP] Java 590
611 611. Valid Triangle Number.java Medium [Array, Two Pointers] O(n^2) O(logn), sorting space Java 591
341 341. Flatten Nested List Iterator.java Medium [Design, NestedInteger, Stack] O(n) O(n) Java 592
254 254. Factor Combinations.java Medium [BFS, Backtracking, DFS] O(x), x is the # of results O(y), y is all ongoing candidates in queue Java 593
739 739. Daily Temperatures.java Medium [Hash Table, Monotonous Stack, Stack] O(n) O(n) Java 594
373 373. Find K Pairs with Smallest Sums.java Medium [Heap, MaxHeap, MinHeap] O(klogk) O(k) Java 595
256 256. Paint House.java Easy [DP, Sequence DP, Status DP] O(nm), m = # of colors O(nm), or O(1) with rolling array Java 596
265 265. Paint House II.java Hard [DP, Sequence DP, Status DP] O(NK^2): O(K) with rolling array Java 597
272 272. Closest Binary Search Tree Value II.java Hard [Stack, Tree] O(n) O(n) Java 598
72 72. Edit Distance.java Hard [DP, Double Sequence DP, Sequence DP, String] O(MN) Java 599
215 215. Kth Largest Element in an Array.java Medium [Divide and Conquer, Heap, MinHeap, PriorityQueue, Quick Select, Quick Sort] O(nlogk) O(k) Java 600