class Solution {
public:
    /**
     * @param nums: a list of integers.
     * @param k: length of window.
     * @return: the sum of the element inside the window at each moving.
     */
    vector<int> winSum(vector<int> &nums, int k) {
        // write your code here
        int n = nums.size();
        if(n<k || k==0) return {};
        int sum = 0;
        for(int i=0;i<k;i++){
            sum += nums[i];
        }
        vector<int> res{sum};
        int l=1, r=k;
        while(r<n){
            sum = sum-nums[l-1]+nums[r];
            res.push_back(sum);
            l++;
            r++;
        }
        return res;
    }
};