Easy
- 1 Two Sum
- 20 Valid Parentheses
- 21 Merge Two Sorted Lists
- 121 Best Time to Buy Sell Stock
- 125 Valid Palindrome
- 226 Invert Binary Tree
- 242 Valid Anagram
- 704 Binary Search
- 733 Flood Fill
- 110 Balanced Binary Tree
- 141 Linked List Cycle
- 232 Implement Queue Using Stacks
- 278 First Bad Version
- 383 Ransom Note
- 70 Climbing Stairs
- 409 Longest Palindrome
- 206 Reverse Linked List
- 169 Majority Element
- 67 Add Binary
- 543 Diameter of Binary Tree
- 876 Middle of the Linked List
- 104 Maximum Depth of Binary Tree
- 217 Contains Duplicate
Medium
- 235 Lowest Common Ancestor of a Binary Search Tree