Given an array of positive integers nums and an integer k,
return true if nums has a continuous subarray whose sum equals k.
Examples:
nums = [1,2,3,4], k = 6 → true
(subarray[1,2,3])nums = [1,2,3,4], k = 8 → false
(no continuous subarray sums to 8)nums = [1], k = 6 → false
Since all numbers are positive, we can use a sliding window:
- Expand the right pointer and accumulate the running sum.
- If the sum exceeds
k, shrink the left pointer. - If it matches
k, return true. - If the loop ends without finding a match, return false.
This works in O(n) because the two pointers only move forward.
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