| Topic | Key Patterns |
|---|---|
| Arrays / Strings | Two pointers Sliding Window Frequency Maps |
| Recursion / Backtracking | Permutations Subsets Constraint building |
| Hashing | Maps Sets |
| Trees / Graphs | BFS / DFS Visited sets Adjacency list modeling |
| Greedy / Sorting | Intervals, prioritization by values |
| Stack / Queue | Monotonic stack Expression evaluation Parentheses |
| Type | Problems |
|---|---|
| Medium classic | 3Sum Longest Substring Without Repeating Characters |
| Graph | Number of Islands Clone Graph |
| DP | Coin Change, House Robber |
| Tree | Lowest Common Ancestor Diameter of Binary Tree |
| Backtracking | Letter Combinations of a Phone Number Word Search |