public static void mergeSort(int[] arr, int left, int right) {
        if (left < right) {
            int mid = (left + right) / 2;
            mergeSort(arr, left, mid);
            mergeSort(arr, mid + 1, right);
            merge(arr, left, mid, right);
        }
    }

    public static void merge(int[] arr, int left, int mid, int right) {
        int i = left, j = mid + 1, length = right - left + 1;
        int[] temp = new int[length];

        int k = 0;

        while (i <= mid && j <= right) {
            if (arr[i] < arr[j])
                temp[k++] = arr[i++];
            else
                temp[k++] = arr[j++];
        }

        while (j <= right)
            temp[k++] = arr[j++];
        while (i <= mid)
            temp[k++] = arr[i++];

        for (k = 0; k < length; k++) {
            arr[left++] = temp[k];
        }
    }