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

using namespace std;

typedef std::deque<int> list_t;

void merge(list_t& lst, list_t left, list_t right)
{
    list_t res;
    while (!left.empty() || !right.empty())
    {
        if (!left.empty() && !right.empty())
        {
            if (left.front() <= right.front())
            {
                res.push_back(left.front());
                left.pop_front();
            }
            else
            {
                res.push_back(right.front());
                right.pop_front();
            }
        }
        else if (!left.empty())
        {
            res.push_back(left.front());
            left.pop_front();
        }
        else if (!right.empty())
        {
            res.push_back(right.front());
            right.pop_front();
        }
    }

    res.swap(lst);
}

void merge_sort(list_t& lst)
{
    size_t n = lst.size();
    if (n <= 1)
        return;

    list_t left, right;
    size_t mpos = n / 2;
    for (size_t i = 0; i < n; ++i)
    {
        if (i < mpos)
            left.push_back(lst[i]);
        else
            right.push_back(lst[i]);
    }

    merge_sort(left);
    merge_sort(right);
    merge(lst, left, right);
}

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 *= 50;
        lst.push_back(val);
    }

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

    return EXIT_SUCCESS;
}