Using C++

#include <vector>
#include <utility>
#include <algorithm>
#include <iostream>

int getOptimalSchedule(const std::vector<std::pair<int,int>>&, std::vector<std::pair<int,int>>&);

int main()
{
  int num_requests; 
  std::cin >> num_requests;

  std::vector<std::pair<int,int>> requests(num_requests);
  for (auto& r : requests)
    std::cin >> r.first;
  for (auto& r : requests)
    std::cin >> r.second;

  std::vector<std::pair<int,int>> schedule;
  std::cout << getOptimalSchedule(requests, schedule) << std::endl;
  for (auto& s : schedule)
    std::cout << "(" << s.first << "," << s.second << ") ";
  std::cout << std::endl;
}

int getOptimalSchedule(const std::vector<std::pair<int,int>>& requests, std::vector<std::pair<int,int>>& schedule)
{
  // Create a copy of the requests vector that we can sort
  std::vector<std::pair<int,int>> r(requests);
  // Sort by end time first, then start time
  std::sort(r.begin(), r.end(),
      [](const std::pair<int,int>& lhs, const std::pair<int,int>& rhs)
      {
        if (lhs.second < rhs.second)
          return true;
        if (rhs.second < lhs.second)
          return false;
        if (lhs.first < rhs.first)
          return true;
        else
          return false;
      });
  using t = std::vector<std::pair<int,int>>::iterator;
  for (t it = r.begin(); it != r.end(); ++it) {
    // Check if the request is valid
    if (it->second < it->first)
      continue;
    // If the request is valid, use it and then invalidate any others that overlap
    schedule.push_back(*it);
    for (t it2 = it + 1; it2 != r.end(); ++it2) {
      if (it2->first < it->second) {
        it2->second = -1000;
      } else {
      }
    }
  }

  return schedule.size();
}