Two Pointer Sliding Window

Sliding window is two pointers where window length changes: fix one violation at a time by moving left after extending right.

Try this in Python

def min_subarray_len(target: int, nums: list[int]) -> int:
    left = 0
    s = 0
    best = 10**9
    for right, x in enumerate(nums):
        s += x
        while s >= target:
            best = min(best, right - left + 1)
            s -= nums[left]
            left += 1
    return 0 if best == 10**9 else best


print(min_subarray_len(7, [2, 3, 1, 2, 4, 3]))

Key takeaways

• Prefix sum inside window is just running sum variable.
• Shrink while valid to find minimum length.
• Beware empty array and impossible case.