#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>

int main()
{
    std::ifstream ifs { "schedule.txt" };

    std::vector<std::pair<int, bool>> events { };
    
    bool arrival { false };
    std::transform(std::istream_iterator<int>{ ifs },
                   std::istream_iterator<int>{ },
                   std::back_inserter(events),
                   [&arrival](int time)
                   {
                       return std::make_pair(time, arrival = !arrival);
                   });

    std::sort(std::begin(events), std::end(events));

    std::vector<int> trains(events.size());
    std::transform(std::begin(events), std::end(events),
                   std::begin(trains),
                   [](std::pair<int, bool> const& p)
                   {
                       if (p.second)
                           return 1;
                       return -1;
                   });

    std::partial_sum(std::begin(trains), std::end(trains), std::begin(trains));
    auto it = std::max_element(std::begin(trains), std::end(trains));

    auto index = std::distance(std::begin(trains), it);
    std::cout << "The maximum occurances are " << *it << " at time point "
              << std::next(std::begin(events), index)->first << std::endl;
}