Sliding Window - Notes

Sliding-window is a go-to for array/string problems with contiguous ranges.

Fixed window: maintain a window of size k (e.g., max sum of k elements). Variable window: expand/contract based on condition (e.g., smallest subarray >= target).

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# smallest subarray with sum >= target (variable window)
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def min_subarray(nums, target):
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  left = 0
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  curr = 0
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  ans = float('inf')
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  for right, v in enumerate(nums):
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    curr += v
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    while curr >= target:
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      ans = min(ans, right - left + 1)
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      curr -= nums[left]
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      left += 1
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  return ans if ans != float('inf') else 0

Tip: prefer O(n) with two pointers when window properties are monotonic.