Subarray Sum Equals K

Given an integer array and target `k`, count all contiguous subarrays whose sum equals `k`. The follow-up checks whether negative numbers break sliding-window assumptions. Examples Example 1: Input: nums = [1,1,1], k = 2 Output: 2 Explanation: The subarrays [1,1] at indices 0..1 and 1..2 both sum to 2. Example 2: Input: nums = [1,2,3], k = 3 Output: 2 Explanation: [1,2] sums to 3 and [3] sums to 3. Example 3: Input: nums = [1,-1,0], k = 0 Output: 3 Explanation: [1,-1], [1,-1,0], and [0] all sum to 0. Constraints 1 <= nums.length <= 2 * 10^4 -1000 <= nums[i] <= 1000 -10^7 <= k <= 10^7