Minimum Size Subarray Sum

Problem:

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous 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.

Analysis:

Sliding window problem. update the window when sum >= s.

Solution:

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        int res = Integer.MAX_VALUE;
        if (nums == null || nums.length == 0) {
            return 0;
        }
        int left = 0,  sum = 0;
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            while (sum >= s) {
                res = Math.min(res, i - left + 1);
                sum -= nums[left++];
            }
        }
        return res == Integer.MAX_VALUE ? 0 : res;
    }
}