Find the Shortest Contiguous Segment Reaching a Sum Threshold

### Problem Return the minimum length of a nonempty contiguous segment of `nums` whose sum is at least `k`. Return `-1` if no segment qualifies. Values may be negative, so extending a segment need not increase its sum. ```cpp class Solution { public: int shortestSubarray(vector<int>& nums, int k); }; ``` ### Examples **Example 1:** ```text Input: nums = [2,-1,2,3], k = 4 Output: 2 Explanation: The last two values sum to 5. No single value reaches 4. ``` **Example 2:** ```text Input: nums = [1,-2,1], k = 2 Output: -1 Explanation: Every segment has sum at most 1. ``` ### Constraints - `1 <= nums.length <= 10^5` - `-10^5 <= nums[i] <= 10^5` - `1 <= k <= 10^9` ### Contract considerations The result is a length, not the segment. Equality with k qualifies. The answer may be -1 even when the total array length is large. ```hint Read the boundary condition Compare two starting prefixes: when does the later start dominate the earlier one? ``` ### Boundary reminders The result is a length, not the segment. Equality with k qualifies. The answer may be -1 even when the total array length is large.