ID	Problem	Solution	Difficulty	Remark
0001	Two Sum	Solution	Easy
0002	Add Two Numbers	Solution	Medium
0003	Longest Substring Without Repeating Characters	Solution	Medium
0004	Median of Two Sorted Arrays	Solution	Hard
0005	Longest Palindromic Substring	Solution	Medium	To Optimize
0006	ZigZag Conversion	Solution	Medium
0007	Reverse Integer	Solution	Easy
0008	String to Integer (atoi)	Solution	Medium	Not Recommend
0009	Palindrome Number	Solution	Easy
0011	Container With Most Water	Solution	Medium
0013	Roman to Integer	Solution	Easy	Not Recommend
0014	Longest Common Prefix	Solution	Easy
0015	3Sum	Solution	Medium
0016	3Sum Closest	Solution	Medium
0017	Letter Combinations of a Phone Number	Solution	Medium
0018	4Sum	Solution	Medium
0019	Remove Nth Node From End of List	Solution	Medium	Double-Pointer
0020	Valid Parentheses	Solution	Easy
0021	Merge Two Sorted Lists	Solution	Easy
0026	Remove Duplicates from Sorted Array	Solution	Easy
0027	Remove Element	Solution	Easy
0035	Search Insert Position	Solution	Easy
0039	Combination Sum	Solution	Medium	Backtracing
0040	Combination Sum II	Solution	Medium	Backtracing
0046	Permutations	Solution	Medium
0047	Permutations	Solution	Medium	Backtracing
0049	Group Anagrams	Solution	Medium
0051	N-Queens	Solution	Hard	BackTracing
0052	N-Queens II	Solution	Hard	BackTracing
0053	Maximum Subarray	Solution	Easy	DP
0062	Unique Paths	Solution	Medium
0063	Unique Paths II	Solution	Medium
0064	Minimum Path Sum	Solution	Medium
0066	Plus One	Solution	Easy
0070	Climbing Stairs	Solution	Easy
0075	Sort Colors	Solution	Medium
0076	Minimum Window Substring	Solution	Hard
0080	Remove Duplicates from Sorted Array II	Solution	Medium
0088	Merge Sorted Array	Solution	Easy
0091	Decode Ways	Solution	Medium
0093	Restore IP Addresses	Solution	Medium
0096	Unique Binary Search Trees	Solution	Medium
0104	Maximum Depth of Binary Tree	Solution	Easy	Recursion
0120	Triangle	Solution	Medium
0121	Best Time to Buy and Sell Stock	Solution	Easy	DP
0122	Best Time to Buy and Sell Stock II	Solution	Easy	DP
0123	Best Time to Buy and Sell Stock III	Solution	Hard	DP
0125	Valid Palindrome	Solution	Medium
0131	Palindrome Partitioning	Solution	Medium
0149	Max Points on a Line	Solution	Hard
0167	Two Sum II - Input array is sorted	Solution	Easy
0188	Best Time to Buy and Sell Stock IV	Solution	Hard	DP
0198	House Robber	Solution	Easy
0199	Binary Tree Right Side View	Solution	Medium	BackTracing
0202	Happy Number	Solution	Easy
0203	Remove Linked List Elements	Solution	Easy
0205	Isomorphic Strings	Solution	Easy
0206	Reverse Linked List	Solution	Easy
0208	Implement Trie (Prefix Tree)	Solution	Medium
0209	Minimum Size Subarray Sum	Solution	Medium
0211	Add and Search Word - Data structure design	Solution	Medium
0213	House Robber II	Solution	Medium
0215	Kth Largest Element in an Array	Solution	Medium
0216	Combination Sum III	Solution	Medium	Backtracing
0217	Contains Duplicate	Solution	Easy
0219	Contains Duplicate II	Solution	Easy
0220	Contains Duplicate III	Solution	Medium
0242	Valid Anagram	Solution	Easy
0279	Valid Anagram	Solution	Medium
0283	Move Zeroes	Solution	Easy
0290	Word Pattern	Solution	Easy
0300	Longest Increasing Subsequence	Solution	Medium
0303	Range Sum Query - Immutable	Solution	Easy
0307	Range Sum Query - Mutable	Solution	Medium
0309	Best Time to Buy and Sell Stock with Cooldown	Solution	Medium	DP
0332	Reconstruct Itinerary	Solution	Medium	Graph
0338	Counting Bits	Solution	Medium
0343	Integer Break	Solution	Medium
0344	Reverse String	Solution	Easy
0345	Reverse Vowels of a String	Solution	Easy
0347	Top K Frequent Elements	Solution	Medium
0349	Intersection of Two Arrays	Solution	Easy
0350	Intersection of Two Arrays II	Solution	Easy
0376	Wiggle Subsequence	Solution	Medium
0438	Find All Anagrams in a String	Solution	Medium
0447	Number of Boomerangs	Solution	Easy
0454	4Sum II	Solution	Medium
0530	Minimum Absolute Difference in BST	Solution	Easy
0557	Reverse Words in a String III	Solution	Easy
0606	Construct String from Binary Tree	Solution	Easy
0677	Map Sum Pairs	Solution	Medium
0700	Search in a Binary Search Tree	Solution	Easy
0783	Minimum Distance Between BST Nodes	Solution	Easy
0804	Unique Morse Code Words	Solution	Easy
0877	Stone Game	Solution	Medium
0938	Range Sum of BST	Solution	Easy
1025	Divisor Game	Solution	Easy