Java Algorithm Problems

程序员的一天

从开始这个Github已经有将近两年时间, 很高兴这个repo可以帮到有需要的人. 我一直认为, 知识本身是无价的, 因此每逢闲暇, 我就会来维护这个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这个repo:

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

Future Milestone: 我准备将一些有意思的题目，做成视频的形式给大家参考

希望大家学习顺利, 对未来充满希望(程序员也是找到好老板的!) 有问题可以给我写邮件([email protected]), 或者在GitHub上发issue给我.

Squence	Problem	Level	Language	Tags	Video Tutorial
0	Count of Smaller Number before itself.java	Hard	Java	[]
1	Count of Smaller Number.java	Review	Java	[Binary Search, Segment Tree]
2	Delete Digits.java	Medium	Java	[]
3	Find the Weak Connected Component in the Directed Graph.java	Medium	Java	[Union Find]
4	Flatten 2D Vector.java	Medium	Java	[Design]
5	Fraction to Recurring Decimal.java	Medium	Java	[Hash Table, Math]
6	Gray Code.java	Medium	Java	[Backtracking]
7	Group Shifted Strings.java	Easy	Java	[]
8	Hamming Distance.java	Easy	Java	[]
9	Happy Number.java	Easy	Java	[]
10	HashHeap.java	Hard	Java	[]
11	HashWithArray.java	Easy	Java	[]
12	Heapify.java	Review	Java	[Heap]
13	Heaters.java	Easy	Java	[]
14	IndexMatch.java	Easy	Java	[]
15	Inorder Successor in Binary Search Tree.java	Medium	Java	[BST, Tree]
16	Insert Node in a Binary Search Tree .java	Easy	Java	[BST]
17	Intersection of Two Arrays.java	Easy	Java	[]
18	Intersection of Two Linked Lists.java	Easy	Java	[Linked List]
19	Interval Sum II.java	Hard	Java	[]
20	Isomorphic Strings.java	Easy	Java	[]
21	Jewels and Stones.java	Easy	Java	[Hash Table]
22	Kth Largest Element.java	Review	Java	[Divide and Conquer, Heap, Quick Sort]
23	Kth Smallest Sum In Two Sorted Arrays.java	Hard	Java	[]
24	LFU Cache.java	Hard	Java	[Design, Hash Table]
25	Longest Univalue Path.java	Easy	Java	[]
26	Majority Number II.java	Medium	Java	[Enumeration, Greedy]
27	Majority Number III.java	Medium	Java	[Hash Table, Linked List]
28	Matrix Zigzag Traversal.java	Easy	Java	[]
29	Maximum Subarray III.java	Review	Java	[]
30	Minimum Absolute Difference in BST.java	Easy	Java	[BST]
31	Minimum Height Trees.java	Medium	Java	[BFS, Graph]
32	Missing Ranges.java	Medium	Java	[Array]
33	Next Permutation.java	Medium	Java	[Array]
34	O(1) Check Power of 2.java	Easy	Java	[Bit Manipulation]
35	Palindrome Permutation II.java	Medium	Java	[Backtracking, Permutation]
36	Partition Array by Odd and Even.java	Easy	Java	[Array, Two Pointers]
37	Pascal's Triangle II.java	Easy	Java	[]
38	Permutation Index.java	Easy	Java	[]
39	Permutation Sequence.java	Medium	Java	[Backtracking, Math]
40	Product of Array Exclude Itself.java	Medium	Java	[Array]
41	Recover Rotated Sorted Array.java	Easy	Java	[Array]
42	Remove Duplicates from Unsorted List.java	Medium	Java	[Linked List]
43	Remove Node in Binary Search Tree.java	Hard	Java	[BST]
44	Reshape the Matrix.java	Easy	Java	[]
45	Reverse String.java	Easy	Java	[]
46	Roman to Integer.java	Easy	Java	[]
47	Rotate Image.java	Medium	Java	[Array, Enumeration]
48	Search Insert Position.java	Easy	Java	[]
49	Search Rotated in Sorted Array II.java	Medium	Java	[Array, Binary Search]
50	Shortest Word Distance.java	Easy	Java	[]
51	Single Number II.java	Medium	Java	[Bit Manipulation]
52	Single Number III.java	Medium	Java	[Bit Manipulation]
53	Single Number.java	Easy	Java	[]
54	Sliding Window Maximum.java	Hard	Java	[]
55	Space Replacement.java	Medium	Java	[String]
56	Stone Game.java	Medium	Java	[DP]
57	String Permutation.java	Easy	Java	[]
58	String to Integer(atoi).java	Easy	Java	[]
59	Strobogrammatic Number.java	Easy	Java	[]
60	Subarray Sum II.java	Hard	Java	[Array, Binary Search, Two Pointers]
61	The Smallest Difference.java	Medium	Java	[Array, Sort, Two Pointers]
62	Total Occurrence of Target.java	Medium	Java	[]
63	Trailing Zeros.java	Easy	Java	[Math]
64	Two Lists Sum.java	Medium	Java	[Linked List]
65	Two Strings Are Anagrams.java	Easy	Java	[]
66	Ugly Number II.java	Medium	Java	[DP, Heap, Math]
67	Valid Parentheses.java	Easy	Java	[]
68	Valid Sudoku.java	Easy	Java	[]
69	Word Ladder II.java	Hard	Java	[]
70	Word Pattern.java	Easy	Java	[]
71	Zigzag Iterator.java	Medium	Java	[BST]
72	Find Anagram Mappings.java	Easy	Java	[Hash Table]
73	Judge Route Circle.java	Easy	Java	[String]
74	Island Perimeter.java	Easy	Java	[Hash Table]
75	First Unique Character in a String.java	Easy	Java	[Hash Table, String]
76	Power of Three.java	Easy	Java	[Math]
77	Plus One.java	Easy	Java	[Array, Math]
78	Power of Two.java	Easy	Java	[Bit Manipulation, Math]
79	Reverse Vowels of a String.java	Easy	Java	[String, Two Pointers]
80	Guess Number Higher or Lower.java	Easy	Java	[Binary Search]
81	Encode and Decode TinyURL.java	Medium	Java	[Hash Table, Math]
82	Wiggle Sort.java	Medium	Java	[Array, Sort]
83	Queue Reconstruction by Height.java	Medium	Java	[Greedy]
84	2 Sum II - Input array is sorted.java	Medium	Java	[Array, Binary Search, Two Pointers]
85	2 Sum II.java	Medium	Java	[Array, Binary Search, Two Pointers]
86	Coin Change.java	Medium	Java	[Backpack DP, DP, Memoization]
87	Maximum Product Subarray.java	Medium	Java	[Array, DP, Subarray]
88	3 Sum Closest.java	Medium	Java	[Array, Two Pointers]
89	Triangle Count.java	Medium	Java	[Array]
90	3 Sum.java	Medium	Java	[Array, Two Pointers]
91	4 Sum.java	Medium	Java	[Hash Table]
92	k Sum.java	Hard	Java	[DP]
93	Unique Binary Search Tree.java	Medium	Java	[BST, DP, Tree]
94	Trim a Binary Search Tree.java	Easy	Java	[BST, Tree]
95	Unique Paths II.java	Medium	Java	[Array, Coordinate DP, DP]
96	Bomb Enemy.java	Medium	Java	[Coordinate DP, DP]
97	3 Sum Smaller.java	Medium	Java	[Array, Two Pointers]
98	Array Partition I.java	Easy	Java	[Array]
99	1-bit and 2-bit Characters.java	Easy	Java	[Array]
100	Non-decreasing Array.java	Easy	Java	[Array]
101	Max Consecutive Ones.java	Easy	Java	[Array]
102	Find All Numbers Disappeared in an Array.java	Easy	Java	[Array]
103	Maximum Average Subarray I.java	Easy	Java	[Array, Subarray]
104	Largest Number At Least Twice of Others.java	Easy	Java	[Array]
105	Toeplitz Matrix.java	Easy	Java	[Array]
106	Sum of Two Integers.java	Easy	Java	[Bit Manipulation]
107	Swap Bits.java	Easy	Java	[Bit Manipulation]
108	Update Bits.java	Medium	Java	[Bit Manipulation]
109	Maximum XOR of Two Numbers in an Array.java	Medium	Java	[Bit Manipulation, Trie]
110	Perfect Squares.java	Medium	Java	[BFS, DP, Math, Partition DP]
111	Backpack VI.java	Medium	Java	[Backpack DP, DP]
112	Copy Books.java	Hard	Java	[Binary Search, DP, Partition DP]
113	Valid Perfect Square.java	Review	Java	[Binary Search, Math]
114	Intersection of Two Arrays II.java	Easy	Java	[Binary Search, Hash Table, Sort, Two Pointers]
115	Scramble String.java	Hard	Java	[DP, Interval DP, String]
116	Binary Search Tree Iterator.java	Medium	Java	[BST, Design, Stack, Tree]
117	Flatten Nested List Iterator.java	Medium	Java	[Design, Stack]
118	Best Time to Buy and Sell Stock with Cooldown.java	Medium	Java	[DP]
119	Find Peak Element.java	Medium	Java	[Array, Binary Search]
120	Longest Common Subsequence.java	Medium	Java	[DP, Double Sequence DP, Sequence DP]
121	Interleaving String.java	Hard	Java	[DP, String]
122	Letter Combinations of a Phone Number.java	Medium	Java	[Backtracking, String]
123	Edit Distance.java	Hard	Java	[DP, Double Sequence DP, Sequence DP, String]
124	Distinct Subsequences.java	Hard	Java	[DP, String]
125	Regular Expression Matching.java	Review	Java	[Backtracking, DP, String]
126	Majority Element.java	Easy	Java	[Array, Bit Manipulation, Divide and Conquer]
127	Wildcard Matching.java	Hard	Java	[Backtracking, DP, Greedy, String]
128	Ones and Zeroes.java	Hard	Java	[DP]
129	Pow(x,n).java	Medium	Java	[Binary Search, Math]
130	Word Break II.java	Hard	Java	[Backtracking, DFS, DP, Memoization]
131	Nested List Weight Sum.java	Easy	Java	[BFS, DFS]
132	Same Tree.java	Easy	Java	[DFS, Tree]
133	Convert Sorted Array to Binary Search Tree.java	Easy	Java	[DFS, Divide and Conquer, Tree]
134	Construct Binary Tree from Inorder and Preorder Traversal.java	Medium	Java	[Array, DFS, Divide and Conquer, Hash Table, Tree]
135	Add Binary.java	Easy	Java	[Math, String]
136	Add Digits.java	Easy	Java	[Math]
137	Add Two Numbers.java	Medium	Java	[Linked List, Math]
138	Add Two Numbers II.java	Medium	Java	[Linked List]
139	Balanced Binary Tree.java	Medium	Java	[DFS, Tree]
140	Valid Anagram.java	Easy	Java	[Hash Table, Sort]
141	Populating Next Right Pointers in Each Node.java	Medium	Java	[DFS, Divide and Conquer, Tree]
142	Validate Binary Search Tree.java	Medium	Java	[BST, DFS, Divide and Conquer, Tree]
143	Convert Sorted List to Binary Search Tree.java	Medium	Java	[BST, DFS, Divide and Conquer, Linked List]
144	Flatten Binary Tree to Linked List.java	Medium	Java	[Binary Tree, DFS]
145	Binary Tree Paths.java	Easy	Java	[Backtracking, Binary Tree, DFS]
146	Minimum Size Subarray Sum.java	Medium	Java	[Array, Binary Search, Subarray, Two Pointers]
147	Clone Graph.java	Medium	Java	[BFS, DFS, Graph]
148	Longest Substring Without Repeating Characters.java	Medium	Java	[Hash Table, String, Two Pointers]
149	Minimum Window Substring.java	Review	Java	[Hash Table, String, Two Pointers]
150	Linked List Cycle.java	Easy	Java	[Linked List, Two Pointers]
151	Remove Nth Node From End of List.java	Medium	Java	[Linked List, Two Pointers]
152	Longest Substring with At Most K Distinct Characters.java	Medium	Java	[Hash Table, String]
153	Linked List Cycle II.java	Medium	Java	[Linked List, Math, Two Pointers]
154	Kth Smallest Number in Sorted Matrix.java	Medium	Java	[Binary Search, Heap]
155	Find Minimum in Rotated Sorted Array.java	Medium	Java	[Array, Binary Search]
156	Find Minimum in Rotated Sorted Array II.java	Hard	Java	[Array, Binary Search]
157	Connecting Graph.java	Medium	Java	[Union Find]
158	Connecting Graph II.java	Medium	Java	[Union Find]
159	Connecting Graph III.java	Medium	Java	[Union Find]
160	Number of Islands.java	Medium	Java	[BFS, DFS, Matrix DFS, Union Find]
161	Number of Islands II.java	Hard	Java	[Union Find]
162	Surrounded Regions.java	Medium	Java	[BFS, DFS, Matrix DFS, Union Find]
163	Implement Trie.java	Medium	Java	[Design, Trie]
164	Add and Search Word.java	Medium	Java	[Backtracking, Design, Trie]
165	Word Search II.java	Hard	Java	[Backtracking, DFS, Trie]
166	Word Search.java	Medium	Java	[Array, Backtracking, DFS]
167	Word Squares.java	Hard	Java	[Backtracking, Trie]
168	Trapping Rain Water.java	Hard	Java	[Array, Stack, Two Pointers]
169	Trapping Rain Water II.java	Hard	Java	[BFS, Heap]
170	Data Stream Median.java	Hard	Java	[Design, Heap]
171	Sliding Window Median.java	Hard	Java	[Design, Heap]
172	Min Stack.java	Easy	Java	[Design, Stack]
173	Implement Queue using Stacks.java	Easy	Java	[Design, Stack]
174	Decode String.java	Medium	Java	[DFS, Divide and Conquer, Stack]
175	Largest Rectangle in Histogram.java	Hard	Java	[Array, Monotonous Stack, Stack]
176	Maximum Binary Tree.java	Medium	Java	[Stack, Tree]
177	Reverse Integer.java	Easy	Java	[Math]
178	Swap Nodes in Pairs.java	Medium	Java	[Linked List]
179	Find Peak Element II.java	Hard	Java	[Binary Search, DFS, Divide and Conquer]
180	Sqrt(x).java	Easy	Java	[Binary Search, Math]
181	First Bad Version.java	Easy	Java	[Binary Search]
182	Wood Cut.java	Medium	Java	[Binary Search]
183	Find the Duplicate Number.java	Medium	Java	[Array, Binary Search, Two Pointers]
184	Palindrome Pairs.java	Hard	Java	[Hash Table, String, Trie]
185	Game of Life.java	Medium	Java	[Array]
186	Maximum Average Subarray II.java	Review	Java	[Array, Binary Search, PreSum]
187	Meeting Rooms.java	Easy	Java	[PriorityQueue, Sort, Sweep Line]
188	Number of Airplane in the sky.java	Medium	Java	[Array, Interval, PriorityQueue, Sort, Sweep Line]
189	Meeting Rooms II.java	Medium	Java	[Greedy, Heap, Sort, Sweep Line]
190	Building Outline.java	Review	Java	[Binary Indexed Tree, Divide and Conquer, Heap, Segment Tree, Sweep Line]
191	Unique Path.java	Medium	Java	[Array, Coordinate DP, DP]
192	Maximal Rectangle.java	Hard	Java	[Array, DP, Hash Table, Stack]
193	Maximal Square.java	Medium	Java	[Coordinate DP, DP]
194	Longest Increasing Path in a Matrix.java	Hard	Java	[Coordinate DP, DFS, DP, Memoization, Topological Sort]
195	Coins in a Line.java	Medium	Java	[DP, Game Theory, Greedy]
196	Coins in a Line II.java	Medium	Java	[Array, DP, Game Theory, Memoization, MiniMax]
197	Binary Tree Inorder Traversal.java	Easy	Java	[Hash Table, Stack, Tree]
198	Binary Tree Postorder Traversal.java	Medium	Java	[Stack, Tree, Two Stacks]
199	Change to Anagram.java	Easy	Java	[String]
200	Classical Binary Search.java	Easy	Java	[Binary Search]
201	Climbing Stairs.java	Easy	Java	[DP, Memoization, Sequence DP]
202	Coins in a Line III.java	Hard	Java	[Array, DP, Game Theory, Interval DP, Memoization]
203	Closest Binary Search Tree Value.java	Easy	Java	[BST, Binary Search, Tree]
204	Compare Version Numbers.java	Medium	Java	[String]
205	Count Complete Tree Nodes.java	Medium	Java	[Binary Search, Tree]
206	Course Schedule.java	Medium	Java	[BFS, Backtracking, DFS, Graph, Topological Sort]
207	Course Schedule II.java	Medium	Java	[BFS, DFS, Graph, Topological Sort]
208	Binary Tree Preorder Traversal.java	Easy	Java	[BFS, DFS, Stack, Tree]
209	Closest Number in Sorted Array.java	Easy	Java	[Binary Search]
210	Complete Binary Tree.java	Easy	Java	[BFS, Tree]
211	Compare Strings.java	Easy	Java	[String]
212	Contains Duplicate.java	Easy	Java	[Array, Hash Table]
213	Contains Duplicate II.java	Easy	Java	[Array, Hash Table]
214	Contains Duplicate III.java	Medium	Java	[BST]
215	Burst Balloons.java	Hard	Java	[DP, Divide and Conquer, Interval DP, Memoization]
216	Nim Game.java	Easy	Java	[Brainteaser, DP, Game Theory]
217	Convert Integer A to Integer B.java	Easy	Java	[Bit Manipulation]
218	Cosine Similarity.java	Easy	Java	[Basic Implementation]
219	Count 1 in Binary.java	Easy	Java	[Bit Manipulation]
220	Count and Say.java	Easy	Java	[Basic Implementation, String]
221	One Edit Distance.java	Medium	Java	[String]
222	K Edit Distance.java	Hard	Java	[DP, Double Sequence DP, Sequence DP, Trie]
223	Jump Game.java	Medium	Java	[Array, DP, Greedy]
224	Coin Change 2.java	Medium	Java	[Backpack DP, DP]
225	Paint House.java	Easy	Java	[DP, Sequence DP, Status DP]
226	Decode Ways.java	Medium	Java	[DP, Partition DP, String]
227	Longest Continuous Increasing Subsequence.java	Easy	Java	[Array, Coordinate DP, DP]
228	Minimum Path Sum.java	Medium	Java	[Array, Coordinate DP, DP]
229	Counting Bits.java	Medium	Java	[Bit Manipulation, Bitwise DP, DP]
230	Continuous Subarray Sum.java	Medium	Java	[Coordinate DP, DP, Math, Subarray]
231	House Robber.java	Easy	Java	[DP, Sequence DP]
232	House Robber II.java	Medium	Java	[DP, Sequence DP, Status DP]
233	House Robber III.java	Medium	Java	[DFS, DP, Status DP, Tree]
234	Paint House II.java	Hard	Java	[DP, Sequence DP, Status DP]
235	Best Time to Buy and Sell Stock III .java	Hard	Java	[Array, DP, Sequence DP]
236	Best Time to Buy and Sell Stock IV.java	Hard	Java	[DP, Sequence DP]
237	Russian Doll Envelopes.java	Hard	Java	[Binary Search, Coordinate DP, DP]
238	Permutation in String.java	Medium	Java	[Two Pointers]
239	Permutations II.java	Medium	Java	[Backtracking]
240	Shuffle an Array.java	Medium	Java	[Permutation]
241	Find All Anagrams in a String.java	Easy	Java	[Hash Table]
242	Group Anagrams.java	Medium	Java	[Hash Table, String]
243	Backpack.java	Medium	Java	[Backpack DP, DP]
244	Backpack II.java	Medium	Java	[Backpack DP, DP]
245	Backpack V.java	Medium	Java	[Backpack DP, DP]
246	Count Primes.java	Easy	Java	[Hash Table, Math]
247	Delete Node in a Linked List.java	Easy	Java	[Linked List]
248	Excel Sheet Column Number.java	Easy	Java	[Math]
249	Excel Sheet Column Title.java	Easy	Java	[Math]
250	Flip Game.java	Easy	Java	[String]
251	Expression Tree Build.java	Hard	Java	[Binary Tree, Expression Tree, Minimum Binary Tree, Stack]
252	Expression Evaluation.java	Hard	Java	[Binary Tree, DFS, Expression Tree, Minimum Binary Tree, Stack]
253	Convert Expression to Polish Notation.java	Hard	Java	[Binary Tree, DFS, Expression Tree, Stack]
254	Convert Expression to Reverse Polish Notation.java	Hard	Java	[Binary Tree, DFS, Expression Tree, Stack]
255	Evaluate Reverse Polish Notation.java	Medium	Java	[Stack]
256	Decode Ways II.java	Hard	Java	[DP, Partition DP]
257	Palindrome Partitioning II.java	Hard	Java	[DP, Partition DP]
258	Backpack III.java	Hard	Java	[Backpack DP, DP]
259	First Missing Positive.java	Hard	Java	[Array]
260	Implement strStr().java	Easy	Java	[String, Two Pointers]
261	Insertion Sort List.java	Medium	Java	[Linked List, Sort]
262	Integer to English Words.java	Hard	Java	[Math, String]
263	Interleaving Positive and Negative Numbers.java	Medium	Java	[Two Pointers]
264	Largest Number.java	Medium	Java	[Sort]
265	Last Position of Target.java	Easy	Java	[Binary Search]
266	Length of Last Word.java	Easy	Java	[String]
267	Longest Common Substring.java	Medium	Java	[DP, Double Sequence DP, Sequence DP, String]
268	Longest Increasing Continuous subsequence.java	Easy	Java	[Array, Coordinate DP, DP]
269	Longest Increasing Continuous subsequence II.java	Medium	Java	[Array, Coordinate DP, DP, Memoization]
270	N-Queens.java	Hard	Java	[Backtracking]
271	N-Queens II.java	Hard	Java	[Backtracking]
272	Maximum Subarray.java	Easy	Java	[Array, DFS, DP, Divide and Conquer, PreSum, Sequence DP, Subarray]
273	Maximum Subarray II.java	Medium	Java	[Array, DP, Greedy, PreSum, Sequence DP, Subarray]
274	Median.java	Easy	Java	[Array, Quick Select, Quick Sort]
275	Merge Sorted Array.java	Easy	Java	[Array, Two Pointers]
276	Middle of Linked List.java	Easy	Java	[Linked List]
277	Singleton.java	Easy	Java	[Design]
278	Remove Linked List Elements.java	Easy	Java	[Linked List]
279	Fibonacci.java	Easy	Java	[DP, Math, Memoization]
280	Palindrome Linked List.java	Easy	Java	[Linked List, Two Pointers]
281	Reverse Linked List.java	Easy	Java	[Linked List]
282	Reverse Linked List II .java	Medium	Java	[Linked List]
283	Palindrome Permutation.java	Easy	Java	[Hash Table]
284	Valid Palindrome.java	Easy	Java	[String, Two Pointers]
285	Implement Stack using Queues.java	Easy	Java	[Design, Stack]
286	Implement Stack.java	Easy	Java	[Stack]
287	Invert Binary Tree.java	Easy	Java	[BFS, DFS, Tree]
288	Maximum Depth of Binary Tree.java	Easy	Java	[DFS, Tree]
289	Minimum Depth of Binary Tree.java	Easy	Java	[BFS, DFS, Tree]
290	Symmetric Tree.java	Easy	Java	[BFS, DFS, Tree]
291	Tweaked Identical Binary Tree.java	Easy	Java	[DFS, Tree]
292	Merge Two Binary Trees.java	Easy	Java	[DFS, Tree]
293	Subtree.java	Easy	Java	[DFS, Tree]
294	Lowest Common Ancestor of a Binary Tree.java	Medium	Java	[DFS, Tree]
295	Lowest Common Ancestor II.java	Easy	Java	[Hash Table, Tree]
296	Lowest Common Ancestor of a Binary Search Tree.java	Medium	Java	[BST, DFS, Tree]
297	Hash Function.java	Easy	Java	[Hash Table]
298	Merge Two Sorted Lists.java	Easy	Java	[Linked List]
299	Missing Number.java	Easy	Java	[Array, Bit Manipulation, Math]
300	LRU Cache.java	Hard	Java	[Design, Hash Table, Linked List]
301	Remove Duplicates from Sorted Array.java	Easy	Java	[Array, Two Pointers]
302	Remove Duplicates from Sorted Array II.java	Medium	Java	[Array, Two Pointers]
303	Remove Duplicates from Sorted List.java	Easy	Java	[Linked List]
304	Remove Duplicates from Sorted List II.java	Medium	Java	[Linked List]
305	QuickSort.java	Medium	Java	[Sort]
306	MergeSort.java	Medium	Java	[Merge Sort, Sort]
307	Longest Word in Dictionary.java	Easy	Java	[Hash Table, Trie]
308	Binary Tree Level Order Traversal.java	Medium	Java	[BFS, DFS, Tree]
309	Binary Tree Level Order Traversal II.java	Medium	Java	[BFS, Tree]
310	Binary Tree Longest Consecutive Sequence II.java	Medium	Java	[DFS, Divide and Conquer, Double Recursive, Tree]
311	Binary Tree Maximum Path Sum.java	Hard	Java	[DFS, DP, Tree, Tree DP]
312	Path Sum.java	Easy	Java	[DFS, Tree]
313	Path Sum II.java	Easy	Java	[Backtracking, DFS, Tree]
314	Path Sum III.java	Easy	Java	[DFS, Double Recursive, Tree]
315	Rotate String.java	Easy	Java	[String]
316	Combinations.java	Medium	Java	[Backtracking, Combination, DFS]
317	Combination Sum IV.java	Medium	Java	[Array, Backpack DP, DP]
318	Binary Tree Right Side View.java	Medium	Java	[BFS, DFS, Tree]
319	Binary Tree Maximum Path Sum II.java	Medium	Java	[DFS, Tree]
320	Rotate List.java	Medium	Java	[Linked List, Two Pointers]
321	Basic Calculator.java	Hard	Java	[Binary Tree, Expression Tree, Math, Minimum Binary Tree, Stack]
322	Longest Consecutive Sequence.java	Hard	Java	[Array, Hash Table, Union Find]
323	Binary Tree Longest Consecutive Sequence.java	Medium	Java	[DFS, Divide and Conquer, Tree]
324	Number of Connected Components in an Undirected Graph.java	Medium	Java	[BFS, DFS, Graph, Union Find]
325	Next Closest Time.java	Medium	Java	[Basic Implementation, Enumeration, String]
326	Serilization and Deserialization Of Binary Tree.java	Hard	Java	[BFS, DFS, Design, Divide and Conquer, Tree]
327	Partition Array.java	Medium	Java	[Array, Quick Sort, Sort, Two Pointers]
328	Word Ladder.java	Medium	Java	[BFS]
329	Unique Word Abbreviation.java	Medium	Java	[Design, Hash Table]
330	Unique Binary Search Tree II.java	Medium	Java	[BST, DP, Divide and Conquer, Tree]
331	Ugly Number.java	Medium	Java	[Math]
332	Top K Frequent Words.java	Medium	Java	[Hash Table, Heap, PriorityQueue, Trie]
333	Segment Tree Build.java	Medium	Java	[Binary Tree, Divide and Conquer, Segment Tree]
334	Segment Tree Build II.java	Medium	Java	[Binary Tree, Divide and Conquer, Segment Tree]
335	Segment Tree Query.java	Medium	Java	[Binary Tree, DFS, Divide and Conquer, Segment Tree]
336	Segment Tree Modify.java	Medium	Java	[Binary Tree, DFS, Divide and Conquer, Segment Tree]
337	Segment Tree Query II.java	Medium	Java	[Binary Tree, DFS, Divide and Conquer, Segment Tree]
338	Count of Smaller Numbers After Self.java	Review	Java	[BST, Binary Indexed Tree, Binary Search, Divide and Conquer, Segment Tree]
339	ColorGrid.java	Medium	Java	[Design, Hash Table]
340	Container With Most Water.java	Medium	Java	[Array, Two Pointers]
341	Copy List with Random Pointer.java	Medium	Java	[Hash Table, Linked List]
342	Encode and Decode Strings.java	Medium	Java	[String]
343	Fast Power.java	Medium	Java	[DFS, Divide and Conquer]
344	Find the Connected Component in the Undirected Graph.java	Medium	Java	[BFS, DFS]
345	HashWithCustomizedClass(LinkedList).java	Medium	Java	[Hash Table]
346	Interval Minimum Number.java	Medium	Java	[Binary Search, Divide and Conquer, Segment Tree]
347	Interval Sum.java	Medium	Java	[Binary Search, Segment Tree]
348	Kth Smallest Element in a BST.java	Medium	Java	[BST, DFS, Stack, Tree]
349	Longest Common Prefix.java	Easy	Java	[String]
350	Majority Element II.java	Medium	Java	[Array]
351	Merge k Sorted Lists.java	Medium	Java	[Divide and Conquer, Heap, Linked List, PriorityQueue]
352	Merge k Sorted Arrays.java	Medium	Java	[Heap, PriorityQueue]
353	Permutations.java	Medium	Java	[Backtracking, DFS, Permutation]
354	Partition List.java	Medium	Java	[Linked List, Two Pointers]
355	Peeking Iterator.java	Medium	Java	[Design]
356	Rehashing.java	Medium	Java	[Hash Table]
357	Reorder List.java	Medium	Java	[Linked List]
358	Restore IP Addresses.java	Medium	Java	[Backtracking, DFS, String]
359	Reverse Words in a String.java	Medium	Java	[String]
360	Reverse Words in a String II.java	Medium	Java	[String]
361	Reverse Words in a String III.java	Easy	Java	[String]
362	Search a 2D Matrix.java	Medium	Java	[Array, Binary Search]
363	Search a 2D Matrix II.java	Medium	Java	[Binary Search, Divide and Conquer]
364	Search for a Range.java	Medium	Java	[Array, Binary Search]
365	Search Range in Binary Search Tree .java	Medium	Java	[BST, Binary Tree]
366	Merge Sorted Array II.java	Easy	Java	[Array]
367	Nth to Last Node in List.java	Easy	Java	[Linked List]
368	Sort List.java	Medium	Java	[Divide and Conquer, Linked List, Merge Sort, Sort]
369	Summary Ranges.java	Medium	Java	[Array]
370	Top K Frequent Elements.java	Medium	Java	[Hash Table, Heap, PriorityQueue]
371	Topological Sorting.java	Medium	Java	[BFS, DFS, Topological Sort]
372	Median of two Sorted Arrays.java	Hard	Java	[Array, Binary Search, DFS, Divide and Conquer]
373	Remove Duplicate Letters.java	Hard	Java	[Greedy, Hash Table, Stack]
374	Spiral Matrix.java	Medium	Java	[Array, Enumeration]
375	Expression Add Operators.java	Hard	Java	[Backtracking, DFS, Divide and Conquer, String]
376	Insert Interval.java	Hard	Java	[Array, PriorityQueue, Sort]
377	Shortest Palindrome.java	Hard	Java	[KMP, String]
378	2 Sum.java	Easy	Java	[Array, Hash Table]
379	K Empty Slots.java	Hard	Java	[Array, BST, TreeSet]
380	Count of Range Sum.java	Hard	Java	[BST, Divide and Conquer, Merge Sort, PreSum]
381	Max Sum of Rectangle No Larger Than K.java	Hard	Java	[Array, BST, Binary Search, DP, Queue, TreeSet]
382	Perfect Rectangle.java	Hard	Java	[Design, Geometry, Hash Table]
383	Construct Binary Tree from Inorder and Postorder Traversal.java	Medium	Java	[Array, DFS, Divide and Conquer, Tree]
384	Generate Parentheses.java	Medium	Java	[Backtracking, DFS, Sequence DFS, String]
385	Strobogrammatic Number II.java	Medium	Java	[DFS, Math, Sequence DFS]
386	Alien Dictionary.java	Hard	Java	[BFS, Backtracking, DFS, Graph, Topological Sort]
387	Flip Game II.java	Medium	Java	[Backtracking, DFS, DP]
388	Max Area of Island.java	Easy	Java	[Array, DFS]
389	Max Points on a Line.java	Hard	Java	[Array, Geometry, Hash Table, Math]
390	Number of Digit One.java	Hard	Java	[Math]
391	Binary Representation.java	Hard	Java	[Bit Manipulation, String]
392	Palindrome Partitioning.java	Medium	Java	[Backtracking, DFS]
393	Graph Valid Tree.java	Medium	Java	[BFS, DFS, Graph, Union Find]
394	Recover Binary Search Tree.java	Hard	Java	[BST, DFS, Tree]
395	Subarray Sum.java	Easy	Java	[Array, Hash Table, PreSum, Subarray]
396	Submatrix Sum.java	Medium	Java	[Array, Hash Table, PreSum]
397	Longest Palindromic Substring.java	Medium	Java	[DP, String]
398	Longest Palindromic Subsequence.java	Medium	Java	[DFS, DP, Interval DP, Memoization]
399	Jump Game II.java	Hard	Java	[Array, Coordinate DP, DP, Greedy]
400	Gas Station.java	Medium	Java	[Greedy]
401	Triangles.java	Medium	Java	[Array, Coordinate DP, DFS, DP, Memoization]
402	Range Sum Query - Immutable.java	Easy	Java	[DP, PreSum]
403	Longest Valid Parentheses.java	Hard	Java	[Coordinate DP, Stack, String]
404	Remove Invalid Parentheses.java	Review	Java	[BFS, DFS, DP]
405	Merge Intervals.java	Medium	Java	[Array, PriorityQueue, Sort, Sweep Line]
406	H-Index.java	Medium	Java	[Bucket Sort, Hash Table, Sort]
407	H-Index II.java	Medium	Java	[Binary Search]
408	Sort Color.java	Medium	Java	[Array, Partition, Sort, Two Pointers]
409	Sort Colors II.java	Medium	Java	[Partition, Sort, Two Pointers]
410	Sort Letters by Case.java	Medium	Java	[Partition, Sort, String, Two Pointers]
411	Subarray Sum Closest.java	Medium	Java	[PreSum, PriorityQueue, Sort, Subarray]
412	Task Scheduler.java	Medium	Java	[Array, Enumeration, Greedy, PriorityQueue, Queue]
413	Rearrange String k Distance Apart.java	Hard	Java	[Greedy, Hash Table, Heap]
414	Exam Room.java	Medium	Java	[PriorityQueue, Sort]
415	Anagrams.java	Medium	Java	[Array, Hash Table]
416	Path Sum IV.java	Medium	Java	[DFS, Hash Table, Tree]
417	Longest Words.java	Easy	Java	[Hash Table, String]
418	Unique Characters.java	Easy	Java	[Array, String]
419	Number Of Corner Rectangles.java	Medium	Java	[DP, Math]
420	Palindromic Substrings.java	Medium	Java	[DP, String]
421	Multiply Strings.java	Medium	Java	[Math, String]
422	Subset.java	Medium	Java	[Array, BFS, Backtracking, Bit Manipulation, DFS]
423	Subsets II.java	Medium	Java	[Array, BFS, Backtracking, DFS]
424	Combination Sum.java	Medium	Java	[Array, Backtracking, Combination, DFS]
425	Combination Sum II.java	Medium	Java	[Array, Backtracking, Combination, DFS]
426	Combination Sum III.java	Medium	Java	[Array, Backtracking, Combination, DFS]
427	Total Hamming Distance.java	Medium	Java	[Bit Manipulation]
428	Smallest Subtree with all the Deepest Nodes.java	Medium	Java	[DFS, Divide and Conquer, Tree]
429	Binary Gap.java	Easy	Java	[Bit Manipulation]
430	Subarray Sum Equals K.java	Medium	Java	[Array, Hash Table, PreSum, Subarray]
431	Maximize Distance to Closest Person.java	Easy	Java	[Array]
432	Simplify Path.java	Medium	Java	[Stack, String]
433	Convert Binary Search Tree to Sorted Doubly Linked List (in place).java	Medium	Java	[BST, DFS, Linked List, Tree]
434	Convert Binary Search Tree to Sorted Doubly Linked List (extra space).java	Medium	Java	[Linked List, Stack, Tree]
435	Paint Fence.java	Easy	Java	[DP, Sequence DP]
436	Binary Tree Zigzag Level Order Traversal.java	Medium	Java	[BFS, Stack, Tree]
437	Word Break.java	Medium	Java	[DP, Sequence DP]
438	Best Time to Buy and Sell Stock I.java	Easy	Java	[Array, DP, Sequence DP]
439	Best Time to Buy and Sell Stock II.java	Easy	Java	[Array, DP, Greedy, Sequence DP, Status DP]
440	Longest Increasing Subsequence.java	Medium	Java	[Binary Search, Coordinate DP, DP, Memoization]
441	Best Time to Buy and Sell Stock with Transaction Fee.java	Medium	Java	[Array, DP, Greedy, Sequence DP, Status DP]
442	Random Pick Index.java	Medium	Java	[Reservior Sampling]
443	Find the Celebrity.java	Medium	Java	[Array, Greedy]
444	Sparse Matrix Multiplication.java	Medium	Java	[Hash Table]
445	Brick Wall.java	Medium	Java	[Hash Table]
446	Walls and Gates.java	Medium	Java	[BFS, DFS]
447	Accounts Merge.java	Medium	Java	[DFS, Hash Table, Union Find]
448	Exclusive Time of Functions.java	Medium	Java	[Stack]
449	Friends Of Appropriate Ages.java	Medium	Java	[Array, Math]
450	Target Sum.java	Medium	Java	[DFS, DP]
451	Maximum Size Subarray Sum Equals k.java	Medium	Java	[Hash Table, PreSum, Subarray]
452	Kth Largest Element in an Array.java	Medium	Java	[Divide and Conquer, Heap]
453	Contiguous Array.java	Medium	Java	[Hash Table]
454	Line Reflection.java	Medium	Java	[Hash Table, Math]
455	Insert Delete GetRandom O(1).java	Medium	Java	[Array, Design, Hash Table]
456	Number of Longest Increasing Subsequence.java	Medium	Java	[Coordinate DP, DP]
457	Minimum Swaps To Make Sequences Increasing.java	Medium	Java	[Coordinate DP, DP, Status DP]
458	Binary Tree Vertical Order Traversal.java	Medium	Java	[BFS, DFS, Hash Table, Tree]
459	Populating Next Right Pointers in Each Node II.java	Medium	Java	[DFS, Tree]
460	Search Rotated in Sorted Array.java	Medium	Java	[Array, Binary Search]
461	Minimum Subarray.java	Easy	Java	[Array, DP, Greedy, Sequence DP, Subarray]