Return the smallest length of a nonempty contiguous subarray of nums whose sum is at least k. If no such subarray exists, return -1. Values in nums may be negative.
Example 1:
Input: nums = [3,-2,5]
k = 4
Output: 1Explanation: The single-element subarray [5] already has sum at least 4, so the shortest length is 1.
Example 2:
Input: nums = [2,-1,2]
k = 3
Output: 3Explanation: The full array has sum 3. Each shorter contiguous subarray has sum below 3, so the answer is 3.
Example 3:
Input: nums = [-2,-1]
k = 1
Output: -1Explanation: Every nonempty subarray has a negative sum. None can reach the positive target 1, so return -1.
Constraints:
1 <= nums.length <= 100000-100000 <= nums[i] <= 1000001 <= k <= 1000000000