➕ Prefix Sum — Index
Parent: Array Index
| Section | Question | Difficulty |
|---|---|---|
| Build Prefix Array | Template | — |
| Range Sum Query | Class-based | Easy |
| Subarray Sum = K | Hash map + prefix | Medium |
| Equilibrium Index | Left = Right sum | Medium |
| Product Except Self | Left/right pass | Medium |
| Max Subarray (Kadane) | Running max | Medium |
| 2D Matrix Sum | 2D prefix | Medium |