Leetcode 1396

class UndergroundSystem {
    HashMap<Integer,Pair<String,Integer>> checkIn;
    HashMap<String,Pair<Double,Integer>> log;
    public UndergroundSystem() {
        checkIn = new HashMap<>();
        log = new HashMap<>();
    }
    
    public void checkIn(int id, String stationName, int t) {
        // check in the customer 
        checkIn.putIfAbsent(id,new Pair<>(stationName,t));
    }
    
    public void checkOut(int id, String stationName, int t) {
        Pair<String,Integer> info = checkIn.get(id);
        String startStation = info.getKey();
        int startTime = info.getValue();
        String route = startStation + "->" + stationName;
        double tripTime = t - startTime;

        if(log.containsKey(route)){
            double loggedTime = log.get(route).getKey();
            int loggedTrip = log.get(route).getValue();
            log.put(route,new Pair<>(tripTime + loggedTime, loggedTrip + 1));
        }else{
            log.put(route,new Pair<>(tripTime,1));
        }
        // remove the entry
        checkIn.remove(id);
    }
    
    public double getAverageTime(String startStation, String endStation) {
        // Lookup how many times this journey has been made, and the total time.
        String routeKey = startStation + "->" + endStation;
        Double totalTime = log.get(routeKey).getKey();
        int totalTrips = log.get(routeKey).getValue();
        // The average is simply the total divided by the number of trips.
        return totalTime / totalTrips;
    }
}

/**
 * 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);
 */