#include <iostream>
#include <vector>
#include <fstream>
#include <unordered_map>
#include <set>

#include <tuple>

typedef std::unordered_multimap<char, char> graph_type;

std::tuple<graph_type, std::set<char>> build_graph()
{
    graph_type graph;
    std::ifstream file("Day7.in");
    std::string line;

    std::set<char> nodes;

    while (std::getline(file, line)) {
        char a = line[5];
        char b = line[36];
        std::cout << "a: " << a << ", b:" << b << std::endl;

        graph.insert({ b, a });

        nodes.insert(a);
        nodes.insert(b);
    }

    return std::make_tuple(graph, nodes);
}

bool node_blocked(graph_type &graph, std::set<char> &to_consider, char node)
{
    auto [start, end] = graph.equal_range(node);
    for (auto pair = start; pair != end; ++pair) {
        char parent = pair->second;
        if (to_consider.count(parent) > 0) {
            return true;
        }
    }

    return false;
}

int main(int argc, char **argv)
{
    auto [graph, to_consider] = build_graph();

    std::vector<char> order;
    while (!to_consider.empty()) {
        for (auto node = to_consider.begin(); node != to_consider.end(); ++node) {
            bool blocked = node_blocked(graph, to_consider, *node);
            if (blocked)
                continue;

            order.push_back(*node);
            std::cout << *node;

            to_consider.erase(node);
            break;
        }
    }
    std::cout << std::endl;

    return 0;
}