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.

public class Solution {
    /**
     * @param nums: an array of integers
     * @param s: an integer
     * @return: an integer representing the minimum size of subarray
     */
    public int minimumSize(int[] nums, int s) {
        // write your code here
        int j = 0, i = 0;
        int sum =0;
        int ans = Integer.MAX_VALUE;
        for(i = 0; i < nums.length; i++) {
            while(j < nums.length && sum < s ) {
                sum += nums[j];
                j ++;
            }
            if(sum >=s)
                ans = Math.min(ans, j - i  );
            sum -= nums[i];
        }
        if(ans == Integer.MAX_VALUE)
            ans = -1;
        return ans;
    }
}