public ArrayList<Integer> windowSum(ArrayList<Integer> A,int k){
   ArrayList<Integer> result = new ArrayList<Integer>();
   if(A.size()==0||A==null||k<=0)
       return result;
    int count =0;
    for(int i=0; i<A.size();i++){
     count++;
     if(count>=k){
        int sum=0;//Pay Attention!!
        for(int j=i;j>=i-k+1;j--){
           sum = sum+A.get(j);
        } 
        result.add(sum);
     }
   }
   return result;
}



//Array
public int[] winSum(int[] nums, int k) {
        int[] res = new int[nums.length - k + 1];
        if(nums.length==0||nums==null||k<=0)
            return nums;
        int count = 0;
        for (int i = 0, z = 0; i < nums.length; i++) {
           count++;
            if (count >= k) {
                int sum = 0;
            for (int j = i; j >= i - k + 1; j-- ){

                 sum += nums[j];
             }
            res[z++] = sum;
            }

        }
        return res;
    }