public static void quickSort(int[] arr, int l, int r) {
        if (l >= r)
            return;

        int ran = arr[l + (int)(Math.random() * ((r - l) + 1))];
        int begin = l;
        int end = r;
        int idx = l;
        while (idx <= r) {
            int val = arr[idx];
            if (val == ran) {
                idx++;
            } else if (val < ran) {
                int temp = arr[l];
                arr[l++] = val;
                arr[idx++] = temp;
            } else {
                int temp = arr[r];
                arr[r--] = val;
                arr[idx] = temp;
            }
        }
        quickSort(arr, begin, l - 1);
        quickSort(arr, r + 1, end);
        return;
    }