Спринт 13. Конструкторы для продвинутых.

#include <algorithm>
#include <cmath>
#include <iostream>
#include <map>
#include <set>

class RouteManager {
public:
    void AddRoute(int start, int finish) {
        reachable_lists_[start].insert(finish);
        reachable_lists_[finish].insert(start);
    }

    int FindNearestFinish(int start, int finish) const {
        int result = abs(start - finish);

        if (!reachable_lists_.count(start)) {
            return result;
        }

        const std::set<int>& reachable_stations = reachable_lists_.at(start);
        auto it = reachable_stations.upper_bound(finish);

        if (it == reachable_stations.begin()) {
            return std::min(result, std::abs(*it - finish));

        } else if (it == reachable_stations.end()) {
            return std::min(result, abs(*std::prev(it) - finish));

        } else {
            return std::min(result, std::min(std::abs(*it - finish), abs(*std::prev(it) - finish)));

        }
    }

private:
    std::map<int, std::set<int>> reachable_lists_;
};

int main() {
    using namespace std::literals;

    RouteManager routes;

    int query_count;
    std::cin >> query_count;

    for (int query_id = 0; query_id < query_count; ++query_id) {
        std::string query_type;
        std::cin >> query_type;
        int start, finish;
        std::cin >> start >> finish;

        if (query_type == "ADD"s) {
            routes.AddRoute(start, finish);
        } else if (query_type == "GO"s) {
            std::cout << routes.FindNearestFinish(start, finish) << "\n"s;
        }
    }
}