1396. Design Underground System

class UndergroundSystem {
public:
        // id -> {station name,time}
        unordered_map<int,pair<string,int>>checkInStation; 

        // Route -> {total time,count}
        unordered_map<string,pair<int,int>> checkOutStation;

    UndergroundSystem() {
    }
    
    void checkIn(int id, string stationName, int t) {
          checkInStation[id] = {stationName,t};
    }
    
    void checkOut(int id, string stationName, int t) {
         
          auto cIn = checkInStation[id];
           checkInStation.erase(id);

           string route = cIn.first + "_" + stationName;

           checkOutStation[route].first += t - cIn.second;
           checkOutStation[route].second += 1;  
    }
    
    double getAverageTime(string startStation, string endStation) {
          
           string route  = startStation + "_" + endStation;
           auto time = checkOutStation[route];

        return (double)time.first/time.second;
    }
};

/**
 * Your UndergroundSystem object will be instantiated and called as such:
 * UndergroundSystem* obj = new UndergroundSystem();
 * obj->checkIn(id,stationName,t);
 * obj->checkOut(id,stationName,t);
 * double param_3 = obj->getAverageTime(startStation,endStation);
 */