ArraysEvidence Contributing
Prefix Sum
Precompute running sums (or products) so range queries or comparisons become O(1) instead of re-scanning.
Practice Problems: 15
Difficulty: 4 Easy·9 Medium·2 Hard
Algorithmic Intuition & Recognition
The Prefix Sum technique is applied when tackling problems characterized by specific invariants in the problem state or constraints:
- Core Strategy: Precompute running sums (or products) so range queries or comparisons become O(1) instead of re-scanning.
- When to use: Look for opportunities where repeated re-computation can be replaced by maintaining monotonic properties, state windows, or relational pointers.
- Interview Signal: Demonstrating this pattern shows mastery of Arrays foundations, reducing worst-case algorithmic complexity.