LeetCode Solutions

My solutions for questions in LeetCode OJ, where you may find the problem description. The source code is self-contained with problem description, solution dicssussion, time and space complexity analysis, and the source code itself. All solutions have passed the LeetCode OJ.

Progress

This repo is under construction. 220+/280 questions completed.

#	Question	Difficulty	Solution
1	Two Sum	Medium
2	Add Two Numbers	Medium
3	Longest Substring Without Repeating Characters	Medium
4	Median of Two Sorted Arrays	Hard
5	Longest Palindromic Substring	Medium
6	ZigZag Conversion	Easy
7	Reverse Integer	Easy
8	String to Integer (atoi)	Easy
9	Palindrome Number	Easy
10	Regular Expression Matching	Hard
11	Container With Most Water	Medium
12	Integer to Roman	Medium
13	Roman to Integer	Easy
14	Longest Common Prefix	Easy
15	3Sum	Medium
16	3Sum Closest	Medium
17	Letter Combinations of a Phone Number	Medium
18	4Sum	Medium
19	Remove Nth Node From End of List	Easy
20	Valid Parentheses	Easy
21	Merge Two Sorted Lists	Easy
22	Generate Parentheses	Medium
23	Merge k Sorted Lists	Hard
24	Swap Nodes in Pairs	Medium
25	Reverse Nodes in k-Group	Hard
26	Remove Duplicates from Sorted Array	Easy
27	Remove Element	Easy
28	Implement strStr()	Easy
29	Divide Two Integers	Medium
30	Substring with Concatenation of All Words	Hard
31	Next Permutation	Medium
32	Longest Valid Parentheses	Hard
33	Search in Rotated Sorted Array	Hard
34	Search for a Range	Medium
35	Search Insert Position	Medium
36	Valid Sudoku	Easy
37	Sudoku Solver	Hard
38	Count and Say	Easy
39	Combination Sum	Medium
40	Combination Sum II	Medium
41	First Missing Positive	Hard
42	Trapping Rain Water	Hard
43	Multiply Strings	Medium
44	Wildcard Matching	Hard
45	Jump Game II	Hard
46	Permutations	Medium
47	Permutations II	Medium
48	Rotate Image	Medium
49	Group Anagrams	Medium
50	Pow(x, n)	Medium
51	N-Queens	Hard
52	N-Queens II	Hard
53	Maximum Subarray	Medium
54	Spiral Matrix	Medium
55	Jump Game	Medium
56	Merge Intervals	Hard
57	Insert Interval	Hard
58	Length of Last Word	Easy
59	Spiral Matrix II	Medium
60	Permutation Sequence	Medium
61	Rotate List	Medium
62	Unique Paths	Medium
63	Unique Paths II	Medium
64	Minimum Path Sum	Medium
65	Valid Number	Hard
66	Plus One	Easy
67	Add Binary	Easy
68	Text Justification	Hard
69	Sqrt(x)	Medium
70	Climbing Stairs	Easy
71	Simplify Path	Medium
72	Edit Distance	Hard
73	Set Matrix Zeroes	Medium
74	Search a 2D Matrix	Medium
75	Sort Colors	Medium
76	Minimum Window Substring	Hard
77	Combinations	Medium
78	Subsets	Medium
79	Word Search	Medium
80	Remove Duplicates from Sorted Array II	Medium
81	Search in Rotated Sorted Array II	Medium
82	Remove Duplicates from Sorted List II	Medium
83	Remove Duplicates from Sorted List	Easy
84	Largest Rectangle in Histogram	Hard
85	Maximal Rectangle	Hard
86	Partition List	Medium
87	Scramble String	Hard
88	Merge Sorted Array	Easy
89	Gray Code	Medium
90	Subsets II	Medium
91	Decode Ways	Medium
92	Reverse Linked List II	Medium
93	Restore IP Addresses	Medium
94	Binary Tree Inorder Traversal	Medium
95	Unique Binary Search Trees II	Medium
96	Unique Binary Search Trees	Medium
97	Interleaving String	Hard
98	Validate Binary Search Tree	Medium
99	Recover Binary Search Tree	Hard
100	Same Tree	Easy
101	Symmetric Tree	Easy
102	Binary Tree Level Order Traversal	Easy
103	Binary Tree Zigzag Level Order Traversal	Medium
104	Maximum Depth of Binary Tree	Easy
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium
106	Construct Binary Tree from Inorder and Postorder Traversal	Medium
107	Binary Tree Level Order Traversal II	Easy
108	Convert Sorted Array to Binary Search Tree	Medium
109	Convert Sorted List to Binary Search Tree	Medium
110	Balanced Binary Tree	Easy
111	Minimum Depth of Binary Tree	Easy
112	Path Sum	Easy
113	Path Sum II	Medium
114	Flatten Binary Tree to Linked List	Medium
115	Distinct Subsequences	Hard
116	Populating Next Right Pointers in Each Node	Medium
117	Populating Next Right Pointers in Each Node II	Hard
118	Pascal's Triangle	Easy
119	Pascal's Triangle II	Easy
120	Triangle	Medium
121	Best Time to Buy and Sell Stock	Medium
122	Best Time to Buy and Sell Stock II	Medium
123	Best Time to Buy and Sell Stock III	Hard
124	Binary Tree Maximum Path Sum	Hard
125	Valid Palindrome	Easy
126	Word Ladder II	Hard
127	Word Ladder	Medium
128	Longest Consecutive Sequence	Hard
129	Sum Root to Leaf Numbers	Medium
130	Surrounded Regions	Medium
131	Palindrome Partitioning	Medium
132	Palindrome Partitioning II	Hard
133	Clone Graph	Medium
134	Gas Station	Medium
135	Candy	Hard
136	Single Number	Medium
137	Single Number II	Medium
138	Copy List with Random Pointer	Hard
139	Word Break	Medium
140	Word Break II	Hard
141	Linked List Cycle	Medium
142	Linked List Cycle II	Medium
143	Reorder List	Medium
144	Binary Tree Preorder Traversal	Medium
145	Binary Tree Postorder Traversal	Hard
146	LRU Cache	Hard
147	Insertion Sort List	Medium
148	Sort List	Medium
149	Max Points on a Line	Hard
150	Evaluate Reverse Polish Notation	Medium
151	Reverse Words in a String	Medium
152	Maximum Product Subarray	Medium
153	Find Minimum in Rotated Sorted Array	Medium
154	Find Minimum in Rotated Sorted Array II	Hard
155	Min Stack	Easy
156	Binary Tree Upside Down	Medium
157	Read N Characters Given Read4	Easy
158	Read N Characters Given Read4 II - Call multiple times	Hard
159	Longest Substring with At Most Two Distinct Characters	Hard
160	Intersection of Two Linked Lists	Easy
161	One Edit Distance	Medium
162	Find Peak Element	Medium
163	Missing Ranges	Medium
164	Maximum Gap	Hard
165	Compare Version Numbers	Easy
166	Fraction to Recurring Decimal	Medium
167	Two Sum II - Input array is sorted	Medium
168	Excel Sheet Column Title	Easy
169	Majority Element	Easy
170	Two Sum III - Data structure design	Easy
171	Excel Sheet Column Number	Easy
172	Factorial Trailing Zeroes	Easy
173	Binary Search Tree Iterator	Medium
174	Dungeon Game	Hard
179	Largest Number	Medium
186	Reverse Words in a String II	Medium
187	Repeated DNA Sequences	Medium
188	Best Time to Buy and Sell Stock IV	Hard
189	Rotate Array	Easy
190	Reverse Bits	Easy
191	Number of 1 Bits	Easy
198	House Robber	Easy
199	Binary Tree Right Side View	Medium
200	Number of Islands	Medium
201	Bitwise AND of Numbers Range	Medium
202	Happy Number	Easy
203	Remove Linked List Elements	Easy
204	Count Primes	Easy
205	Isomorphic Strings	Easy
206	Reverse Linked List	Easy
207	Course Schedule	Medium
208	Implement Trie (Prefix Tree)	Medium
209	Minimum Size Subarray Sum	Medium
210	Course Schedule II	Medium
211	Add and Search Word - Data structure design	Medium
212	Word Search II	Hard
213	House Robber II	Medium
214	Shortest Palindrome	Hard
215	Kth Largest Element in an Array	Medium
216	Combination Sum III	Medium
217	Contains Duplicate	Easy
218	The Skyline Problem	Hard
219	Contains Duplicate II	Easy
220	Contains Duplicate III	Medium
221	Maximal Square	Medium
222	Count Complete Tree Nodes	Medium
223	Rectangle Area	Easy
224	Basic Calculator	Medium
225	Implement Stack using Queues	Easy
226	Invert Binary Tree	Easy
227	Basic Calculator II	Medium
228	Summary Ranges	Easy
229	Majority Element II	Medium
230	Kth Smallest Element in a BST	Medium
231	Power of Two	Easy
232	Implement Queue using Stacks	Easy
233	Number of Digit One	Medium
234	Palindrome Linked List	Easy
235	Lowest Common Ancestor of a Binary Search Tree	Easy
236	Lowest Common Ancestor of a Binary Tree	Medium
237	Delete Node in a Linked List	Easy
238	Product of Array Except Self	Medium
239	Sliding Window Maximum	Hard
240	Search a 2D Matrix II	Medium
241	Different Ways to Add Parentheses	Medium
242	Valid Anagram	Easy
243	Shortest Word Distance	Easy
244	Shortest Word Distance II	Medium
245	Shortest Word Distance III	Medium
246	Strobogrammatic Number	Easy
247	Strobogrammatic Number II	Medium
248	Strobogrammatic Number III	Hard
249	Group Shifted Strings	Easy
250	Count Univalue Subtrees	Medium
251	Flatten 2D Vector	Medium
252	Meeting Rooms	Easy
253	Meeting Rooms II	Medium
254	Factor Combinations	Medium
255	Verify Preorder Sequence in Binary Search Tree	Medium
256	Paint House	Medium
257	Binary Tree Paths	Easy
258	Add Digits	Easy
259	3Sum Smaller	Medium
260	Single Number III	Medium
261	Graph Valid Tree	Medium
263	Ugly Number	Easy
264	Ugly Number II	Medium
265	Paint House II	Hard
266	Palindrome Permutation	Easy
267	Palindrome Permutation II	Medium
268	Missing Number	Medium
269	Alien Dictionary	Hard
270	Closest Binary Search Tree Value	Easy
271	Encode and Decode Strings	Medium
272	Closest Binary Search Tree Value II	Hard
273	Integer to English Words	Medium
274	H-Index	Medium
275	H-Index II	Medium
276	Paint Fence	Easy
277	Find the Celebrity	Medium
278	First Bad Version	Easy
279	Perfect Squares	Medium
280	Wiggle Sort	Medium
281	Zigzag Iterator	Medium
282	Expression Add Operators	Hard
283	Move Zeroes	Easy
284	Peeking Iterator	Medium
285	Inorder Successor in BST	Medium
286	Walls and Gates	Medium
287	Find the Duplicate Number	Hard
288	Unique Word Abbreviation	Easy

License

The content of this project is released under the Creative Commons Attribution 3.0 license, and the source code is released under the MIT license.