import java.util.HashMap;

import java.util.Map;

public class ParkingLot {

private final int totalParkingLots;

private Map<Receipt, Car> carMap = new HashMap<Receipt, Car>();

public ParkingLot(int totalParkingLots) {

this.totalParkingLots = totalParkingLots;

}

public int getAvailableParkingLotNumber() {

return totalParkingLots - carMap.size();

}

public Receipt park(Car car) {

if (getAvailableParkingLotNumber() > 0) {

Receipt receipt = new Receipt();

carMap.put(receipt, car);

return receipt;

}

return null;

}

public Car retrieve(Receipt receipt) {

return carMap.get(receipt);

}

private Double calculateVacancyRate() {

return Double.valueOf(getAvailableParkingLotNumber() / totalParkingLots);

}

boolean isVacancyRateHigher(ParkingLot highestVacancyRateParkingLot) {

return calculateVacancyRate() > highestVacancyRateParkingLot.calculateVacancyRate();

}

boolean hasMoreAvailableParkingLots(ParkingLot mostParkingLot) {

return getAvailableParkingLotNumber() > mostParkingLot.getAvailableParkingLotNumber();

}

}