Design Underground System LeetCode solution in Java

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class Passenger {
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  int checkinTime;
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  int checkoutTime;
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  String checkinLocation;
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  String checkoutLocation;
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  public Passenger(String checkinLocation, int checkinTime) {
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    this.checkinLocation = checkinLocation;
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    this.checkinTime = checkinTime;
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  }
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  void checkout(String checkoutLocation, int checkoutTime) {
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    this.checkoutLocation = checkoutLocation;
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    this.checkoutTime = checkoutTime;
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  }
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}
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class Route {
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  String startStation;
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  String endStation;
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  int totalNumberOfTrips;
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  long totalTimeSpentInTrips;
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  public Route(String startStation, String endStation) {
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    this.startStation = startStation;
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    this.endStation = endStation;
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  }
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  double getAverageTime() {
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    return (double) totalTimeSpentInTrips / totalNumberOfTrips;
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  }
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  void addTrip(int startTime, int endTime) {
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    totalTimeSpentInTrips += endTime - startTime;
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    totalNumberOfTrips++;
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  }
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}
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class UndergroundSystem {
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  Map<Integer, Passenger> currentPassengerMap;
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  Map<String, Route> routeMap;
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  public UndergroundSystem() {
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    currentPassengerMap = new HashMap<>();
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    routeMap = new HashMap<>();
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  }
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  public void checkIn(int id, String stationName, int t) {
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    if (!currentPassengerMap.containsKey(id)) {
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      Passenger passenger = new Passenger(stationName, t);
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      currentPassengerMap.put(id, passenger);
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    }
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  }
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  public void checkOut(int id, String stationName, int t) {
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    if (currentPassengerMap.containsKey(id)) {
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      Passenger passenger = currentPassengerMap.get(id);
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      passenger.checkout(stationName, t);
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      String routeKey = passenger.checkinLocation + "," + passenger.checkoutLocation;
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      Route route =
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          routeMap.getOrDefault(
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              routeKey, new Route(passenger.checkinLocation, passenger.checkoutLocation));
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      route.addTrip(passenger.checkinTime, passenger.checkoutTime);
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      routeMap.put(routeKey, route);
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      currentPassengerMap.remove(id);
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    }
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  }
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  public double getAverageTime(String startStation, String endStation) {
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    return routeMap.get(startStation + "," + endStation).getAverageTime();
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  }
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}