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.

在一个数组中，找到一个长度最小的子数组，使它的和大于或等于给定的数字s。我们采用类似滑动窗口的方法来解决。从第一个元素开始，一直累加到和sum大于或等与s，然后我们记录这时的长度。接下来从开始的元素缩小这个窗口，缩小到sum小于s的时候，窗口向右移动，直到移动到数组末尾结束。代码如下：

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