#include <iostream>
#include <future>
#include <vector>
#include <list>
#include <numeric>
#include <iterator>

using namespace std;


template<typename T, typename M1, typename M2>
auto map_reduce(T p, T q, M1 f1, M2 f2,  size_t threads) -> decltype(f1(*p)) {
    vector<future<decltype(f1(*p))> > futures;
    typename T::difference_type len = std::distance(p, q);
    auto doAsyncWork = [len, threads, f1, f2](T p, T q, size_t k) -> decltype(f1(*p)){
        p = next(p, k * (len / threads));
        q = (k < threads - 1) ? next(p, (k + 1) * (len / threads)) : q;
        typename T::difference_type len2 = std::distance(p, q);
        auto res = f1(*p);
        while(++p != q)
            res = f2(res, f1(*p));
        //cout << "k= " << k << " res= " << res << " len= " << len2 << endl;
        return res;
    };

    for(size_t i = 0; i < threads; ++i) {
        auto f = std::async(std::launch::deferred, doAsyncWork, p, q, i);
        futures.push_back(std::move(f));
    }

    //cout << futures.size() << endl;
    //cout << std::distance(p, q) << endl;
    auto p1 = futures.begin();
    auto p2 = ++p1;
    auto kek1 = p1->get();
    auto kek2 = futures.begin()->get();
    //cout << reinterpret_cast<int*>(p1) << " " << reinterpret_cast<int*>(p2) << endl;
    auto ans = f2(kek1, kek2);
    p2++;

    for(; p2 != futures.end(); p2++) {
        auto kek = p2->get();
        ans = f2(ans, kek);
    }

    return ans;
}

int main()
{
    std::list<int> l = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    // параллельное суммирование в 3 потока
    auto sum = map_reduce(l.begin(), l.end(), [](int i){return i;}, std::plus<int>(), 3);
    cout << sum << endl;
    return 0;
}