(leetcode)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.

使用两个指针，start，end，当sum（start，end） < s时，就end++；

否则，将start前移知道找到第一个sum<s的start，并记录最小长度end-start，每次更新最小

class Solution {
public:
// 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.
    int retmin(int a,int b)
    {
        return a<b?a:b;
    }
    int minSubArrayLen(int s, vector<int>& nums) {
        int start = 0;
        int end = 0;
        int sum = 0;
        int min = INT_MAX;

        while(start<nums.size() && end<nums.size())
        {
            while(sum < s && end < nums.size()) sum+=nums[end++];
            while(sum >= s && start <= end) 
            {
                min = retmin(min,end-start);
                sum -= nums[start++];
            }
            
        }
        return min==INT_MAX ?0:min;
    }
};