209 Minimum Size Subarray Sum

来源：Leetcode

原帖：https://leetcode.com/problems/minimum-size-subarray-sum/

题目：
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.

代码：

 class Solution {  
 public:  
   int minSubArrayLen(int s, vector<int>& nums) {  
     if (nums.empty()) return 0;  
     int res = INT_MAX, sum = 0;  
     int start = 0, end = 0;  
     while (end < nums.size()) {  
       sum += nums[end];  
       if (sum < s) {  
         end++; continue;  
       }  
       while (start <= end) {  
         if (sum - nums[start] >= s) {  
           sum -= nums[start++];  
         } else {  
           break;  
         }  
       }  
       res = min(res, end-start+1);  
       end++;  
     }  
     return sum < s ? 0 : res;  
   }  
 };