Two Pointers (Arrays, Strings)
1) 88. Merge Sorted Array
2) 125. Valid Palindrome
3) 680. Valid Palindrome II
4) 26. Remove Duplicates from Sorted Array
5) 283. Move Zeroes
6) 344. Reverse String
7) 167. Two Sum II - Input Array Is Sorted
8) 15. 3Sum
9) 18. 4Sum
10) 1570. Dot Product of Two Sparse Vectors
11) 443. String Compression
HashMap/HashSet
12) 1. Two Sum
13) 1207. Unique Number of Occurrences
14) 169. Majority Element
15) 242. Valid Anagram
16) 953. Verifying an Alien Dictionary
17) 771. Jewels and Stones
18) 560. Subarray Sum Equals K
19) 49. Group Anagrams
20) 380. Insert Delete GetRandom O(1)
Strings (others)
21) 67. Add Binary
22) 859. Buddy Strings
23) 205. Isomorphic Strings
24) 345. Reverse Vowels of a String
25) 5. Longest Palindromic Substring
26) 22. Generate Parentheses
LinkedLists
27) 21. Merge Two Sorted Lists
28) 206. Reverse Linked List
29) 234. Palindrome Linked List
30) 83. Remove Duplicates from Sorted List
31) 138. Copy List with Random Pointer
32) 19. Remove Nth Node From End of List
33) 146. LRU Cache
Binary Search
34) 69. Sqrt(x)
35) 704. Binary Search
36) 278. First Bad Version
37) 162. Find Peak Element
38) 852. Peak Index in a Mountain Array
39) 875. Koko Eating Bananas
Stack
40) 20. Valid Parentheses
41) 232. Implement Queue using Stacks
42) 1249. Minimum Remove to Make Valid Parentheses
43) 445. Add Two Numbers II
44) 71. Simplify Path
45) 155. Min Stack
46) 227. Basic Calculator II
Queues
47) 933. Number of Recent Calls
48) 362. Design Hit Counter
49) 353. Design Snake Game
Heap/PriorityQueue
50) 703. Kth Largest Element in a Stream
51) 215. Kth Largest Element in an Array
52) 347. Top K Frequent Elements
53) 973. K Closest Points to Origin
Binary Tree
54) 94. Binary Tree Inorder Traversal
55) 501. Find Mode in Binary Search Tree
56) 543. Diameter of Binary Tree
57) 101. Symmetric Tree
58) 111. Minimum Depth of Binary Tree
59) 938. Range Sum of BST
60) 104. Maximum Depth of Binary Tree
61) 226. Invert Binary Tree
62) 110. Balanced Binary Tree
63) 314. Binary Tree Vertical Order Traversal
64) 1650. Lowest Common Ancestor of a Binary Tree III
65) 1361. Validate Binary Tree Nodes
66) 236. Lowest Common Ancestor of a Binary Tree
67) 515. Find Largest Value in Each Tree Row
68) 98. Validate Binary Search Tree
69) 199. Binary Tree Right Side View
70) 426. Convert Binary Search Tree to Sorted Doubly Linked List
71) 102. Binary Tree Level Order Traversal
72) 109. Convert Sorted List to Binary Search Tree
Graphs (DFS/BFS)
73) 733. Flood Fill
74) 200. Number of Islands
75) 463. Island Perimeter
76) 547. Number of Provinces
77) 785. Is Graph Bipartite?
78) 277. Find the Celebrity
79) 695. Max Area of Island
80) 934. Shortest Bridge
81) 339. Nested List Weight Sum
Graphs (Topological Sort)
82) 207. Course Schedule
83) 2115. Find All Possible Recipes from Given Supplies
Dynamic Programming
84) 509. Fibonacci Number
85) 121. Best Time to Buy and Sell Stock
86) 70. Climbing Stairs
87) 118. Pascal's Triangle
88) 322. Coin Change
89) 139. Word Break
90) 1048. Longest String Chain
91) 72. Edit Distance
92) 64. Minimum Path Sum
93) 343. Integer Break
94) 91. Decode Ways
95) 1027. Longest Arithmetic Subsequence
96) 42. Trapping Rain Water
97) 198. House Robber
98) 1143. Longest Common Subsequence
99) 276. Paint Fence
100) 62. Unique Paths