| 110. Balanced Binary Tree | solution | easy, bfs, trees |
| 102. Binary Tree Level Order Traversal | solution | Medium, bfs, trees |
| 107. Binary Tree Level Order Traversal II | solution | easy, bfs, trees |
| 101. Symmetric Tree | solution | easy, dfs, trees |
| 103. Binary Tree Zigzag Level Order Traversal | solution | Medium, bfs, trees |
| 199. Binary Tree Right Side View | solution | Medium, bfs, trees |
| 111. Minimum Depth of Binary Tree | solution | Easy, dfs, trees |
| 112. Path Sum | solution | Easy, bfs, trees |
| 113. Path Sum II | solution | Medium, bfs, backtrack, trees |
| 114. Flatten Binary Tree to Linked List | solution | Medium, bfs, trees |
| 100. Same Tree | solution | Easy, trees, bfs |
| 110. Balanced Binary Tree | solution | easy, tree, dfs |
| 1. Two Sum | solution | Easy, HashTable |
| 136. Single Number | solution | Easy, HashTable |
| 202. Happy Number | solution | Easy, Math, HashTable |
| 217. Contains Duplicate | solution | Easy, HashTable, Sets |
| 219. Contains Duplicate II | solution | Easy, HashTable |
| 1207. Unique Number of Occurrences | solution | Easy, HashTable |
| 13. Roman to Integer | solution | Easy, Strings |
| 151. Reverse Words in a String | solution | Medium, Strings |
| 14. Longest Common Prefix | solution | Easy, Strings |
| 67. Add Binary | solution | Easy, Strings |
| 22. Generate Parentheses | solution | Medium, Backtrack, Strings |
| 53. Maximum Subarray | solution | Easy, Dynamic Programming |
| 121. Best Time to Buy and Sell Stock | solution | Easy, Dynamic Programming |
| 122. Best Time to Buy and Sell Stock II | solution | Easy, Dynamic Programming |
| 62. Unique Paths | solution | Medium, Dynamic Programming |
| 120. Triangle | solution | Medium, Dynamic Programming |
| 49. Group Anagrams | solution | Medium, HashTable |
| 283. Move Zeroes | solution | Easy, Array |
| 844. Backspace String Compare | solution | Easy, String, Stack |
| 155. Min Stack | solution | Easy, Array, Stack |
| 543. Diameter of Binary Tree | solution | Easy, Trees, DFS |
| 5. Longest Palindromic Substring | solution | Medium, Strings |
| 144. Binary Tree Preorder Traversal | solution | Medium, dfs, trees |
| 94. Binary Tree Inorder Traversal | solution | Medium, dfs, trees |
| 739. Daily Temperatures | solution | Medium, Stack, Arrays |
| 3. Longest Substring Without Repeating Characters | solution | Medium, String, Arrays |
| 2. Add Two Numbers | solution | Medium, LinkedList |
| 300. Longest Increasing Subsequence | solution | Medium, Dynamic Programming |
| 46. Permutations | solution | Medium, Backtracking |
| 230. Kth Smallest Element in a BST | solution | Medium, Binary Search Tree, dfs |
| 56. Merge Intervals | solution | Medium, Arrays |
| 133. Clone Graph | solution | Medium, Graph |
| 841. Keys and Rooms | solution | Medium, Graph |