[LeetCode 解题报告]209. Minimum Size Subarray Sum

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s. If there isn't one, return 0 instead.

Example: 

Input: s = 7, nums = [2,3,1,2,4,3]
Output: 2
Explanation: the subarray [4,3] has the minimal length under the problem constraint.

Follow up:

If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n). 

class Solution {
public:
    int minSubArrayLen(int s, vector<int>& nums) {
        if (nums.empty())
            return 0;
        
        int left = 0, right = 0, sum = 0, res = INT_MAX;
        while(right < nums.size()) {
            while(sum < s && right < nums.size()) {
                sum += nums[right++];
            }
            while (sum >= s) {
                res = min(res, right-left);
                sum -= nums[left++];
            }
        }
        
        if (res == INT_MAX)
            return 0;
        else
            return res;
    }
};