public void MaxSum()
        {
            int[]         arr           = { 1, 4, 2, 10, 2, 3, 1, 0, 20 };
            int           k             = 4;
            int           n             = arr.Length;
            SlidingWindow SlidingWindow = new SlidingWindow();

            SlidingWindow.maxSum(arr, n, k);
        }