leetcode.209. 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.

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