#include <cstdlib>
#include <cstring>
#include <iostream>
#include <deque>

using namespace std;

typedef std::deque<int> list_t;

size_t partition(list_t& lst, size_t left, size_t right, size_t pivot)
{
    if (left == right)
        return left;

    list_t::value_type pivot_val = lst[pivot];
    swap(lst[pivot], lst[right]); // move pivot to end.
    size_t store_pos = left;
    for (size_t i = left; i <= right-1; ++i)
    {
        if (lst[i] < pivot_val)
        {
            swap(lst[i], lst[store_pos]);
            ++store_pos;
        }
    }
    swap(lst[store_pos], lst[right]); // Move pivot to its final place.
    return store_pos;
}

void quick_sort_run(list_t& lst, size_t left, size_t right)
{
    if (left >= right)
        return;

    if (right - left == 1)
    {
        // There is only 2 elements.
        if (lst[left] > lst[right])
            swap(lst[left], lst[right]);
        return;
    }

    // There should be at least 3 elements in this segment.

    size_t pivot = right - left == 2 ? left + 1 : (left+right) / 2;

    pivot = partition(lst, left, right, pivot);

    if (pivot == left)
    {
        quick_sort_run(lst, left, pivot);
        quick_sort_run(lst, pivot+1, right);
    }
    else
    {
        quick_sort_run(lst, left, pivot-1);
        quick_sort_run(lst, pivot+1, right);
    }
}

void quick_sort(list_t& lst)
{
    size_t n = lst.size();
    if (n <= 1)
        // Nothing to do.
        return;

    quick_sort_run(lst, 0, n-1);
}

void print_list(const list_t& lst, const char* caption)
{
    cout << caption << ": ";
    for (list_t::const_iterator i = lst.begin(), ie = lst.end(); i != ie; ++i)
        cout << *i << " ";
    cout << endl;
}

int main(int argc, char** argv)
{
    if (argc < 2)
    {
        cout << "needs at least one argument" << endl;
        return EXIT_FAILURE;
    }

    const char* p = argv[1];
    const char* pend = p + strlen(p);
    char* endptr = NULL;
    long list_size = strtol(p, &endptr, 10);
    if (endptr != pend)
    {
        cout << "invalid number: " << p << endl;
        return EXIT_FAILURE;
    }

    cout << "list size: " << list_size << endl;

    list_t lst;
    for (int i = 0; i < list_size; ++i)
    {
        double val = rand();
        val /= RAND_MAX;
        val *= 100;
        lst.push_back(val);
    }

    print_list(lst, "original");
    quick_sort(lst);
    print_list(lst, "sorted");

    return EXIT_SUCCESS;
}