LeetCode 209 Minimum Size Subarray Sum

Problem:

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.

Summary:

找到数组中和大于目标值s的最短子序列。

Solution:

用两个指针分别代表当前子序列的开始和结尾，若计算出的sum小于s，则end++，否则start--，每计算出一个更短的子序列，更新res值。

 class Solution {
 public:
     int minSubArrayLen(int s, vector<int>& nums) {
         int len = nums.size();
         int res = len + , start = , end = , sum = ;
         while (start < len && end < len) {
             while (sum < s && end < len) {
                 sum += nums[end++];
             }

             while (sum >= s && start <= end) {
                 res = min(res, end - start);
                 sum -= nums[start++];
             }
         }

         return res == len +  ?  : res;
     }
 };