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, int[] a) {

        if (a == null || a.length == 0)

            return 0;

  

        int i = 0, j = 0, sum = 0, min = Integer.MAX_VALUE;

  

        while (j < a.length) {

            sum += a[j++];

            while (sum >= s) {

                min = Math.min(min, j - i);

                sum -= a[i++];

            }

        }

  

        return min == Integer.MAX_VALUE ? 0 : min;

    }

}