LeetCode862. Shortest Subarray with Sum at Least K——单调队列

一、题目

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.

Example 1:

Input: nums = [1], k = 1
Output: 1
Example 2:

Input: nums = [1,2], k = 4
Output: -1
Example 3:

Input: nums = [2,-1,2], k = 3
Output: 3

Constraints:

1 <= nums.length <= 105
-105 <= nums[i] <= 105
1 <= k <= 109

二、题解

class Solution {
public:
    int shortestSubarray(vector<int>& nums, int k) {
        int n = nums.size();
        deque<int> q;
        int res = INT_MAX;
        vector<long long> sum(n+1,0);
        for(int i = 0;i < n;i++){
            sum[i+1] = sum[i] + nums[i];
        }
        for(int r = 0;r <= n;r++){
            while(!q.empty() && sum[r] - sum[q.front()] >= k){
                res = min(res,r - q.front());
                q.pop_front();
            }
            while(!q.empty() && sum[q.back()] >= sum[r]) q.pop_back();
            q.push_back(r);
        }
        return res == INT_MAX ? -1 : res;
    }
};