Minimum Size Subarray Sum

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

For example, given the array [2,3,1,2,4,3] and s = 7,
the subarray [4,3] has the minimal length under the problem constraint.

Analyse: Two pointers.

Runtime: 8ms.

class Solution {
public:
    int minSubArrayLen(int s, vector<int>& nums) {
        int start = 0, end = 0;
        int result = INT_MAX, sum = 0;
        bool flag = false;
        for(; end < nums.size(); end++){
            sum += nums[end];
            while(sum >= s){
                flag = true;
                result = min(result, end - start + 1);
                sum -= nums[start++];
            }
        }
        return flag ? result : 0;
    }
};