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.

class Solution {
public:
    int minSubArrayLen(int s, vector<int>& nums) {
        int size = nums.size();
        int minLen = INT_MAX,sum=0;
        int firstPos = 0;
        for(int i=0;i<size;i++){
            sum += nums[i];
            while(sum >= s){
                minLen = min(minLen,i-firstPos+1);
                sum -= nums[firstPos++];
            }
        }
        if(minLen == INT_MAX){
            return 0;
        }else{
            return minLen;
        }
    }
};