862. Shortest Subarray with Sum at Least K

Given an integer array nums and an integer k, return the length of the shortest non-empty subarray of nums with a sum of at least k. If there is no such subarray, return -1.

A subarray is a contiguous part of an array.

class Solution {
public:
    int shortestSubarray(vector<int>& nums, int k) {
        deque<pair<long, int>> dq {{0, -1}};
        int res = INT_MAX;
        long sum = 0;
        for(int i = 0; i < nums.size(); i++) {
            sum += nums[i];

            while(!dq.empty() and dq[0].first <= sum - k)
                res = min(res, i - dq[0].second), dq.pop_front();
            
            while(!dq.empty() and dq.back().first >= sum)
                dq.pop_back();
            
            dq.push_back({sum, i});
        }
        return res == INT_MAX ? -1 : res;
    }
};