209. Minimum Size Subarray Sum(双指针)

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.

Example: 

Input: [2,3,1,2,4,3], s = 7
Output: 2
Explanation: the subarray [4,3] has the minimal length under the problem constraint.

 1 class Solution {
 2     public int minSubArrayLen(int target, int[] a) {
 3         if(a.length==0||a.length==1)
 4             return 0;
 5         int i = 0,j = 0,sum =0 ,min = Integer.MAX_VALUE;
 6         while(j<a.length){
 7             sum+=a[j++];
 8             while(sum>=target){
 9                 min = Math.min(min,j-i);
10                 sum-=a[i++];
11             }
12         }
13         return min==Integer.MAX_VALUE?0:min;
14     }
15     
16 }