Leetcode Problem difficulty level and frequency table(zz)

Source: http://leetcode.cloudfoundry.com/
Author: peking2

Leetcode Questions

Id	Question	Difficulty	Freqency	Data Structures	Algorithms
1	Two Sum	2	5	array set	sort two pointers
2	Add Two Numbers	3	4	linked list	two pointers math
3	Longest Substring Without Repeating Characters	3	2	string hashtable	two pointers
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 heap	sort 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 linked list red-black tree	sort merge
57	Insert Interval	4	5	array linked list red-black tree	sort merge
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 hashtable	recursion 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 tree	bfs stack
104	Maximum Depth of Binary Tree	1	1	tree	dfs
105	Construct Binary Tree from Preorder and Inorder Tr	3	3	array tree	dfs
106	Construct Binary Tree from Inorder and Postorder T	3	3	array tree	dfs
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

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