void quicksort2(iter begin, iter end) {
    if (begin + 1 != end && begin != end) {
        iter end3 = partition2(begin, end, (((*begin) + (*(end - 1)) +
            (*(begin + (end - begin) / 2)))) / 3.0);
        quicksort2(begin, end3);
        quicksort2(end3, end);
    }
}