209. Minimum Size Subarray Sum

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.

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Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

这道题使用两个指针，一个在前面遍历，累加前面的指针，一旦sum超过s，累减慢的指针，直到sum小于s为止，并且每次判断min和i-start，代码如下：

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