- 3 Longest Substring Without Repeating Characters
- 20 Valid Parentheses
- 22 Generate Parentheses
- 47 Permutations II: Recursion
- 56 Merge Intervals
- 80 Remove Duplicates from Sorted Array II: Pointer
- 81 Search in Rotated Sorted Array II
- 98 Validate Binary Search Tree: DFS
- 111 Minimum Depth of Binary Tree: Queue
- 116 Populating Next Right Pointers in Each Node
- 133 Clone Graph: Dictionary
- 142 Linked List Cycle II
- 147 Insertion Sort List
- 150 Evaluate Reverse Polish Notation: Stack
- 173 Binary Search Tree Iterator: Stack
- 188 Best Time to Buy and Sell Stock IV: DP
- 205 Isomorphic Strings: Array
- 228 Summary Ranges
- 334 Increasing Triplet Subsequence
- 337 House Robber III: DP
- 394 Decode String: Stack
- 445 Add Two Numbers II: Stack
- 454 4Sum II: Dictionary
- 456 132 Pattern: Stack
- 458 Poor Pigs: Math Power
- 530 Minimum Absolute Difference in BST: Inorder traversal
- 557 Reverse Words in a String III: Stack
- 563 Binary Tree Tilt: PostOrder
- 593 Valid Square: HashSet
- 653 Two Sum IV Input is a BST: DFS
- 673 Number of Longest Increasing Subsequence
- 735 Asteroid Collision: Stack
- 799 Champgane Tower: DP
- 804 Unique Morse Code Words: HashSet
- 832 Flipping an Image
- 845 Longest Mountain in Array
- 849 Maximize Distance to Closest Person
- 858 Mirror Reflection
- 865 Smallest Subtree with all the Deepest Nodes: DFS
- 880 Decoded String at Index
- 938 Range Sum of BST: PreOrder
- 948 Bag of Tokens: Two-pointer
- 977 Squares of a Sorted Array: Two Pointer
- 1007 Minimum Domino Rotations For Equal Row
- 1026 Maximum Difference Between Node and Ancestor: DFS
- 1217 Minimum Cost to Move Chips to The Same Position: Modulo
- 1290 Convert Binary Number in a Linked List to Integer
- 1323 Maximum 69 Number: CharArray
- 1436 Destination City: Dictionary
- 1446 Consecutive Characters
- 1510 Stone Game IV: DP
- 595 Big Countries: OR or UNION
- 178 Rank Scores: dense_rank()