➕ Prefix Sum — Index
Parent: JS Array Index
| Section | Description |
|---|---|
| Core Concept | Build prefix array, range sum formula |
| Q1. Range Sum Query | Class-based O(1) query |
| Q2. Subarray Sum = K | Prefix + Map |
| Q3. Equilibrium Index | Left sum = right sum |
| Q4. Product Except Self | Left/right prefix products |
| Q5. Kadane's Algorithm | Max subarray sum |
| Q6. 2D Prefix Sum | Matrix range queries |