ParkingLot.java

public enum VehicleSize {
	Compact(1);
	Large(2);
	
	private final int size;
	
	VehicleSize(int size) {
		this.size = size;
	}
	
	public int getSize() {
		return size;
	}
	
}


public abstract class Vehicle {
	public abstract VehicleSize getSize();
}

public class Car extends Vehicle {
	@Override 
	public VehicleSize getSize() {
		return VehicleSize.Compact;
	}
}

public class Truck extends Vehicle {
	@Override
	public VehicleSize getSize() {
		return VehicleSize.Large;
	}
}

class ParkingSpot {
	private final VehicleSize size;
	private Vehicle currentVehicle;
	
	ParkingSpot(VehicleSize size) {
		this.size = size;
	}
	
	boolean fit(Vehicle v) {
		return currentVehicle == null && size.getSize() >= v.getSize().getSize();
	}
	
	/**record a vehicle is parked in by updating the currentVehicle field*/
	void park(Vehicle v) {
		currentVehicle = v;
	}
	
	void leave() {
		currentVehicle = null;
	}
	
	Vehicle getVehicle() {
		return currentVehicle;
	}
}

class Level {
	private final List<ParkingSpot> spots;
	
	Level(int numOfSpots) {
		List<ParkingSpot> list = new ArrayList<>(numOfSpots);
		int i = 0;
		for (; i < numOfSpots / 2; i++) {
			list.add(new ParkingSpot(VehicleSize.Compact));
		}
		for (; i < numOfSpots; i++) {
			list.add(new ParkingSpot(VehicleSize.Large));
		}
		spots = Collections.unmodifiableList(list);
	}
	
	boolean hasSpot(Vehicle v) {
		for (ParkingSpot s : spots) {
			if (s.fit(v)) {
				return true;
			}
		}
		return false;
	}
	
	boolean park(Vehicle v) {
		for (ParkingSpot s : spots) {
			if (s.fit(v)) {
				s.park(v);
				return true;
			}
		}
		return false;
	}
	
	boolean leave(Vehicle v) {
		for (ParkingSpot s : spots) {
			if (s.getVehicle() == v) {
				s.leave();
				return true;
			}
		}
		return false;
	}
}

public class ParkingLot {
	private fianl Level[] levels;
	
	public ParkingLot(int numLevels, int numSpotsPerLevel) {
		levels = new Level[numLevels];
		for (int i = 0; i < numLevels; i++) {
			levels[i] = new Level(numSpotsPerLevel);
		}
	}
	
	public boolean hasSpot(Vehicle v) {
		for (Level l : levels) {
			if (l.hasSpot(v)) {
				return true;
			}
		}
		return false;
	}
	
	public boolean park(Vehicle v) {
		for (Level l : levels) {
			if (l.park(v)) {
				return true;
			}
		}
		return false;
	}
	
	public boolean leave(Vehicle v) {
		for (Level l : levels) {
			if (l.leave(v)) {
				return true;
			}
		}
		return false;
	}
}

class Test {
	public static void main(String[] args) {
		ParkingLot lot = new ParkingLot(4, 10);
		List<Vehicle> list = new ArrayList<>();
		for (int i = 0; i < 50; i++) {
			final Vehicle v = i % 2 == 0 ? new Car() : new Truck();
			list.add(v);
			boolean hasSpot = lot.hasSpot(v);
			if (i < 40) {
				// make sure you enable assert if using it for test
				assert hasSpot;
				assert  lot.park(v);
			} else {
				assert !hasSpot;
				assert !lot.park(v);
			}
		}
		assert list.size() == 50;
		int i = 0;
		for (Vehicle v : list) {
			assert i >= 40 || lot.leave(v);
			i++;
		}
	}
}