#include <iostream>
#include <cstdio>
#include <list>
#include <thread>
#include <memory>
#include <algorithm>
#include <future>

std::ostream& operator<<(std::ostream& ostr, const std::list<int>& list)
{
    for (auto &i : list) {
        ostr << " " << i;
    }
    return ostr;
}

template<typename T>
std::list<T> sequential_quick_sort(std::list<T> input)
{
    if(input.empty())
    {
        return input;
    }
    std::list<T> result;
    result.splice(result.begin(),input,input.begin());
    T const& pivot=*result.begin();
    auto divide_point=std::partition(input.begin(),input.end(),
        [&](T const& t){return t<pivot;});
    std::list<T> lower_part;
    lower_part.splice(lower_part.end(),input,input.begin(),
        divide_point);
    auto new_lower(
        sequential_quick_sort(std::move(lower_part)));
    auto new_higher(
        sequential_quick_sort(std::move(input)));
    result.splice(result.end(),new_higher);
    result.splice(result.begin(),new_lower);
    return result;
}

template<typename T>
std::list<T> parallel_quick_sort(std::list<T> input)
{
    if(input.empty())
    {
        return input;
    }
    std::list<T> result;
    result.splice(result.begin(),input,input.begin());
    T const& pivot=*result.begin();
    auto divide_point=std::partition(input.begin(),input.end(),
        [&](T const& t){return t<pivot;});
    std::list<T> lower_part;
    lower_part.splice(lower_part.end(),input,input.begin(),
        divide_point);
    std::future<std::list<T> > new_lower(
        std::async(&parallel_quick_sort<T>,std::move(lower_part)));
    auto new_higher(
        parallel_quick_sort(std::move(input)));
    result.splice(result.end(),new_higher);
    result.splice(result.begin(),new_lower.get());
    return result;
}

int main()
{
    std::list<int> list1 = {4, 2, 1, 5, 8, 9, 7};
    std::list<int> sorted1 = sequential_quick_sort(list1);
    std::list<int> sorted2 = parallel_quick_sort(list1);
    std::cout << "sorted1: " << sorted1 << std::endl;
    std::cout << "sorted2: " << sorted2 << std::endl;
    return 0;
}