Minimum Size Subarray Sum: the skills you need first

Updated Oct 7, 2026

LeetCode · medium · sliding window. Expand until the sum is enough, then shrink for the shortest cover.

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Skills this problem builds on

Stuck on Minimum Size Subarray Sum? It is usually one of these. Get each one solid and the solution stops being a trick.

1. Shrink to the smallest valid window

   Once sum ≥ S, shrink while the window stays valid. Each successful exclude shortens a still-valid window. Stop when the next exclude would break S.

2. Maintain the sum of the window

   Window sum updates in O(1) per move: add a[R] when R advances, subtract a[L] when L advances. After every move, sum equals a[L]+…+a[R].

3. Track the best valid bounds

   When a valid window beats bestLen, save bestL and bestR (and the new length). The answer slice is a[bestL..bestR], not just a number.

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