Imagine scanning a row of lockers, each holding a number, looking left to right through a peephole that shows exactly k lockers at a time — in every peephole view you note the first negative number you spot.

Formally, given an integer array nums and an integer k, return an array of length n - k + 1 where the element at index i is the first negative number in the subarray nums[i..i+k-1]. If a window contains no negative number, record 0 for that position.

Edge cases: if k <= 0 or k > nums.length, return an empty array.