Leetcode Problem Summary (algorithm, difficulty, frequency)

Id	Question	Difficulty	Frequency	Data Structures	Algorithms
1	The Sum of	2	5	Array + Set	Sort + pointers
2	ADD Numbers	3	4	Linked list	Pointers + Math
3	Longest Substring without repeating characters	3	2	String + hashtable	Pointers
4	Median of 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	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	Pointers
16	3Sum Closest	3	1	Array	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	Pointers
20	Valid parentheses	2	5	String	Stack
21st	Merge Sorted Lists	2	5	Linked list	Sort + pointers + merge
22	Generate parentheses	3	4	String	Dfs
23	Merge k Sorted Lists	3	4	Linked list + heap	Sort + pointers + merge
24	Swap Nodes in Pairs	2	4	Linked list
25	Reverse Nodes in K-group	4	2	Linked list	Recursion + pointers
26	Remove Duplicates from Sorted Array	1	3	Array	Pointers
27	Remove Element	1	4	Array	Pointers
28	Implement StrStr ()	4	5	String	Pointers + KMP + rolling Hash
29	Divide integers	4	3		Binary search + Math
30	Substring with concatenation of all Words	3	1	String	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	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	Pointers + Stack
43	Multiply Strings	4	3	String	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	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	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 + pointers
76	Minimum Window Substring	4	2	String	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	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 + 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	Pointers
87	Scramble String	5	2	String	Recursion + DP
88	Merge Sorted Array	2	5	Array	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	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 + 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	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

Leetcode Problem Summary (algorithm, difficulty, frequency)