problem:209. 长度最小的子数组

思路：维护窗口里面的sum<=k即可

Accode:

class Solution {
public:
    int minSubArrayLen(int target, vector<int>& nums) {
        long long sum =0;
        int ans =1e6;
        int len  =nums.size();
        for(int i=0,j=0;i<len;i++){
            sum+=nums[i];
            while(sum>=target){
                if(sum>=target) ans = min(ans,i-j+1);
                sum-=nums[j];
                ++j;
            }
        }
        return ans==1e6?0:ans;
    }
};

时间复杂度：$o(n)$