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

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