LeetCode 209. Minimum Size Subarray Sum

class Solution {
public:
    int minSubArrayLen(int s, vector<int>& nums) {
        int n = nums.size();
        if (n == 0)
            return 0;
        int i = 0,j = -1 ;   //[i..j] is sliding window
        int res = n +1;
        int sum = 0;
        
        
        while(i < n){
            if( j+1 < n && sum < s ){
                sum += nums[++j];
            }else{
                 sum = sum - nums[i++];
            }
            if (sum >= s)
                res = min( res , j-i+1 );   //update now length 
        }
        
        if(res == n+1)   // 
            return 0;
        return res;
    }
};