public static int partition(int arr[], int left, int right) {
    // Pick a pivot point. Can be any element.
    int pivot = arr[(left + right) / 2];

    while (left <= right) {
        while (arr[left] < pivot) {
            left++;
        }

        while (arr[right] > pivot) {
            right--;
        }

        if (left <= right) {
            swap(arr, left, right);
            left++;
            right--;
        }
    }

    return left;
}