https://wid-blog.github.io/en/tags/prefix-sum/Recent content in Prefix Sum on wid's blogHugoenSun, 14 Jun 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/tech/algorithm/sliding-window-and-prefix-sum/Sun, 14 Jun 2026 00:00:00 +0000https://wid-blog.github.io/en/posts/tech/algorithm/sliding-window-and-prefix-sum/Subarray-sum problems collapse from O(N²) to O(N) along two paths — sliding window or prefix sum with a hash. Negative inputs or strict-equality conditions break monotonicity and shift the work from sliding window to prefix sum.