leetcode难度及面试频率

刷题顺序： 

出现频度为5： 
1. Leet Code OJ 1. Two Sum [Difficulty: Easy] 
2. Leet Code OJ 8. String to Integer (atoi) [Difficulty: Easy] 
3. Leet Code OJ 15. 3Sum [Difficulty: Medium] 
4. Leet Code OJ 20. Valid Parentheses [Difficulty: Easy] 
5. Leet Code OJ 21. Merge Two Sorted Lists [Difficulty: Easy] 
6. Leet Code OJ 28. Implement strStr() [Difficulty: Easy] 
7. Leet Code OJ 56. Merge Intervals [Difficulty: Hard] 
8. Leet Code OJ 57. Insert Interval [Difficulty: Hard] 
9. Leet Code OJ 65. Valid Number [Difficulty: Hard] 
10. Leet Code OJ 70. Climbing Stairs [Difficulty: Easy] 
11. Leet Code OJ 73. Set Matrix Zeroes [Difficulty: Medium] 
12. Leet Code OJ 88. Merge Sorted Array [Difficulty: Easy] 
13. Leet Code OJ 98. Validate Binary Search Tree [Difficulty: Medium] 
14. Leet Code OJ 125. Valid Palindrome [Difficulty: Easy] 
15. Leet Code OJ 127. Word Ladder [Difficulty: Medium]

出现频度为4： 
1. Leet Code OJ 2. Add Two Numbers [Difficulty: Medium] 
2. Leet Code OJ 12. Integer to Roman 
3. Leet Code OJ 13. Roman to Integer 
4. Leet Code OJ 22. Generate Parentheses 
5. Leet Code OJ 23. Merge k Sorted Lists 
6. Leet Code OJ 24. Swap Nodes in Pairs 
7. Leet Code OJ 27. Remove Element [Difficulty: Easy] 
8. Leet Code OJ 46. Permutations 
9. Leet Code OJ 49. Anagrams 
10. Leet Code OJ 67. Add Binary 
11. Leet Code OJ 69. Sqrt(x) 
12. Leet Code OJ 77. Combinations 
13. Leet Code OJ 78. Subsets 
14. Leet Code OJ 79. Word Search 
15. Leet Code OJ 91. Decode Ways [Difficulty: Medium] 
16. Leet Code OJ 102. Binary Tree Level Order Traversal [Difficulty: Easy] 
17. Leet Code OJ 129. Sum Root to Leaf Numbers 
18. Leet Code OJ 131. Palindrome Partitioning

以上转载自： http://blog.youkuaiyun.com/lnho2015/article/details/50962989

	1	Two Sum	2	5	array	sort
					set	Two Pointers
	2	Add Two Numbers	3	4	linked list	Two Pointers
						Math
	3	Longest Substring Without Repeating Characters	3	2	string	Two Pointers
					hashtable
	4	Median of Two Sorted Arrays	5	3	array	Binary Search
	5	Longest Palindromic Substring	4	2	string
	6	ZigZag Conversion	3	1	string
	7	Reverse Integer	2	3		Math
	8	String to Integer (atoi)	2	5	string	Math
	9	Palindrome Number	2	2		Math
	10	Regular Expression Matching	5	3	string	Recursion
						DP
	11	Container With Most Water	3	2	array	Two Pointers
	12	Integer to Roman	3	4		Math
	13	Roman to Integer	2	4		Math
	14	Longest Common Prefix	2	1	string
	15	3Sum	3	5	array	Two Pointers
	16	3Sum Closest	3	1	array	Two Pointers
	17	Letter Combinations of a Phone Number	3	3	string	DFS
	18	4Sum	3	2	array
	19	Remove Nth Node From End of List	2	3	linked list	Two Pointers
	20	Valid Parentheses	2	5	string	Stack
	21	Merge Two Sorted Lists	2	5	linked list	sort
						Two Pointers
						merge
	22	Generate Parentheses	3	4	string	DFS
	23	Merge k Sorted Lists	3	4	linked list	sort
					heap	Two Pointers
						merge
	24	Swap Nodes in Pairs	2	4	linked list
	25	Reverse Nodes in k-Group	4	2	linked list	Recursion
						Two Pointers
	26	Remove Duplicates from Sorted Array	1	3	array	Two Pointers
	27	Remove Element	1	4	array	Two Pointers
	28	Implement strStr()	4	5	string	Two Pointers
						KMP
						rolling hash
	29	Divide Two Integers	4	3		Binary Search
						Math
	30	Substring with Concatenation of All Words	3	1	string	Two Pointers
	31	Next Permutation	5	2	array	permutation
	32	Longest Valid Parentheses	4	1	string	DP
	33	Search in Rotated Sorted Array	4	3	array	Binary Search
	34	Search for a Range	4	3	array	Binary Search
	35	Search Insert Position	2	2	array
	36	Valid Sudoku	2	2	array
	37	Sudoku Solver	4	2	array	DFS
	38	Count and Say	2	2	string	Two Pointers
	39	Combination Sum	3	3	array	combination
	40	Combination Sum II	4	2	array	combination
	41	First Missing Positive	5	2	array	sort
	42	Trapping Rain Water	4	2	array	Two Pointers
						Stack
	43	Multiply Strings	4	3	string	Two Pointers
						Math
	44	Wildcard Matching	5	3	string	Recursion
						DP
						greedy
	45	Jump Game II	4	2	array
	46	Permutations	3	4	array	permutation
	47	Permutations II	4	2	array	permutation
	48	Rotate Image	4	2	array
	49	Anagrams	3	4	string
					hashtable
	50	Pow(x, n)	3	5		Binary Search
						Math
	51	N-Queens	4	3	array	DFS
	52	N-Queens II	4	3	array	DFS
	53	Maximum Subarray	3	3	array	DP
	54	Spiral Matrix	4	2	array
	55	Jump Game	3	2	array
	56	Merge Intervals	4	5	array	sort
					linked list	merge
					red-black tree
	57	Insert Interval	4	5	array	sort
					linked list	merge
					red-black tree
	58	Length of Last Word	1	1	string
	59	Spiral Matrix II	3	2	array
	60	Permutation Sequence	5	1		permutation
						Math
	61	Rotate List	3	2	linked list	Two Pointers
	62	Unique Paths	2	3	array	DP
	63	Unique Paths II	3	3	array	DP
	64	Minimum Path Sum	3	3	array	DP
	65	Valid Number	2	5	string	Math
	66	Plus One	1	2	array	Math
	67	Add Binary	2	4	string	Two Pointers
						Math
	68	Text Justification	4	2	string
	69	Sqrt(x)	4	4		Binary Search
	70	Climbing Stairs	2	5		DP
	71	Simplify Path	3	1	string	Stack
	72	Edit Distance	4	3	string	DP
	73	Set Matrix Zeroes	3	5	array
	74	Search a 2D Matrix	3	3	array	Binary Search
	75	Sort Colors	4	2	array	sort
						Two Pointers
	76	Minimum Window Substring	4	2	string	Two Pointers
	77	Combinations	3	4		combination
	78	Subsets	3	4	array	Recursion
						combination
	79	Word Search	3	4	array	DFS
	80	Remove Duplicates from Sorted Array II	2	2	array	Two Pointers
	81	Search in Rotated Sorted Array II	5	3	array	Binary Search
	82	Remove Duplicates from Sorted List II	3	3	linked list	Recursion
						Two Pointers
	83	Remove Duplicates from Sorted List	1	3	linked list
	84	Largest Rectangle in Histogram	5	2	array	Stack
	85	Maximal Rectangle	5	1	array	DP
						Stack
	86	Partition List	3	3	linked list	Two Pointers
	87	Scramble String	5	2	string	Recursion
						DP
	88	Merge Sorted Array	2	5	array	Two Pointers
						merge
	89	Gray Code	4	2		combination
	90	Subsets II	4	2	array	Recursion
						combination
	91	Decode Ways	3	4	string	Recursion
						DP
	92	Reverse Linked List II	3	2	linked list	Two Pointers
	93	Restore IP Addresses	3	3	string	DFS
	94	Binary Tree Inorder Traversal	4	3	tree	Recursion
					hashtable	morris
						Stack
	95	Unique Binary Search Trees II	4	1	tree	DP
						DFS
	96	Unique Binary Search Trees	3	1	tree	DP
	97	Interleaving String	5	2	string	Recursion
						DP
	98	Validate Binary Search Tree	3	5	tree	DFS
	99	Recover Binary Search Tree	4	2	tree	DFS
	100	Same Tree	1	1	tree	DFS
	101	Symmetric Tree	1	2	tree	DFS
	102	Binary Tree Level Order Traversal	3	4	tree	BFS
	103	Binary Tree Zigzag Level Order Traversal	4	3	queue	BFS
					tree	Stack
	104	Maximum Depth of Binary Tree	1	1	tree	DFS
	105	Construct Binary Tree from Preorder and Inorder Tr	3	3	array	DFS
					tree
	106	Construct Binary Tree from Inorder and Postorder T	3	3	array	DFS
					tree
	107	Binary Tree Level Order Traversal II	3	1	tree	BFS
	108	Convert Sorted Array to Binary Search Tree	2	3	tree	DFS
	109	Convert Sorted List to Binary Search Tree	4	3	linked list	Recursion
						Two Pointers
	110	Balanced Binary Tree	1	2	tree	DFS
	111	Minimum Depth of Binary Tree	1	1	tree	DFS
	112	Path Sum	1	3	tree	DFS
	113	Path Sum II	2	2	tree	DFS
	114	Flatten Binary Tree to Linked List	3	3	tree	Recursion
						Stack
	115	Distinct Subsequences	4	2	string	DP
	116	Populating Next Right Pointers in Each Node	3	3	tree	DFS
	117	Populating Next Right Pointers in Each Node II	4	2	tree	DFS
	118	Pascal's Triangle	2	1	array
	119	Pascal's Triangle II	2	1	array
	120	Triangle	3	1	array	DP
	121	Best Time to Buy and Sell Stock	2	1	array	DP
	122	Best Time to Buy and Sell Stock II	3	1	array	greedy
	123	Best Time to Buy and Sell Stock III	4	1	array	DP
	124	Binary Tree Maximum Path Sum	4	2	tree	DFS
	125	Valid Palindrome	2	5	string	Two Pointers
	126	Word Ladder II	1	1
	127	Word Ladder	3	5	graph	BFS
						shortest path
	128	Longest Consecutive Sequence	4	3	array
	129	Sum Root to Leaf Numbers	2	4	tree	DFS
	130	Surrounded Regions	4	3	array	BFS
						DFS
	131	Palindrome Partitioning	3	4	string	DFS
	132	Palindrome Partitioning II	4	3	string	DP

转载自： LeetCode Question Difficulty Distribution