| 1 | Two Sum |  |  |  | O(nlogn) | O(1) | Array,Hash Table |
| 2 | Add Two Numbers | | |  | O(max(m,n)) | O(1) | Linked List,Math,Recursion |
| 5 | Longest Palindromic Substring | | | | O(n²) | O(n²) | String,DP |
| 20 | Valid Parentheses | | | | O(n) | O(n) | String,Stack |
| 21 | Merge Two Sorted Lists | | | | O(n) | O(n) | Linked List,Recursion |
| 23 | Merge K Sorted Lists | | |  | O(nlogk) | O(n) | Linked List,Divide And Conquer,Priority Queue,Merge Sort |
| 42 | Trapping Rain Water | | | | O(n) | O(1) | Array,Two Pointers,DP,Stack |
| 127 | Word Ladder | | | | O(nm²) | O(nm) | BFS,Hash Table,String |
| 138 | Copy List With Random Pointers | | | | O(n) | O(1) | Hash Table,Linked List |
| 146 | LRU Cache | | | | O(1) | O(1) | Hash Table,Linked List,Design,Doubly Linked List |
| 200 | Number Of Islands | | | | O(mn) | O(min(m,n)) | Array,BFS,DFS,Matrix,Union Find |
| 295 | Find Median From Data Stream | | | | O(logn) | O(n) | Two Pointers,Design,Sorting,Priority Queue,Data Stream |
| 297 | Serialize And Deserialize Binary Tree | | | | O(n) | O(n) | String,Tree,Dfs,Bfs,Design,Binary Tree |
| 692 | Top K Frequent Words | | | | O(nlogn) | O(n) | Hash Table,String,Trie,Sorting,Priority Queue,Bucket Sort,Counting |
| 763 | Partition Labels | | | | O(n) | O(n) | Hash Table,Two Pointers,String,Greedy |
| 819 | Most Common Word | | | | O(n+m) | O(n+m) | Hash Table,String |
| 937 | Reorder Data In Log Files | | | | O(nlogn) | O(n) | Array,String,Sorting |
| 973 | K Closest Points To Origin | | | | O(nlogn) | O(n) | Array,Math,Divide And Conquer,Geometry,Sorting,Priority Queue,Quick Select |
| 994 | Rotting Oranges | | | | O(mn) | O(mn) | Array,BFS,Matrix |
| 1192 | Critical Connections In A Network | | | | O(E+V) | O(E+V) | DFS,Graph,Biconnected Components |