Class identification (ParkingLot, Floor, Spot, Vehicle) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the primary responsibility of the ParkingLot class

In a parking lot system, which of the following best describes the main responsibility of the ParkingLot class?

A Represent a single floor within the parking lot

B Represent a single parking spot where a vehicle can park

C Manage the overall parking facility including floors and spots

D Track the details of a vehicle such as license plate and type

💡 Hint

Think about which class would oversee the entire parking structure.

The ParkingLot class manages the entire parking facility, including multiple floors and parking spots. Other classes represent smaller components.

🧠 Conceptual

intermediate

Which class should handle vehicle parking logic?

In the parking lot system, which class is best suited to handle the logic of parking a vehicle into a spot?

A Floor

B Spot

C Vehicle

D ParkingLot

💡 Hint

Consider which class represents the place where a vehicle actually parks.

The Spot class represents a parking spot and should handle parking and freeing the spot for vehicles.

❓ Architecture

advanced

Determine the correct relationship between Floor and Spot classes

Which of the following best describes the relationship between Floor and Spot classes in a parking lot system?

A Spot inherits from Floor to reuse properties

B Spot contains multiple Floor objects representing levels

C Floor and Spot are unrelated and operate independently

D Floor contains multiple Spot objects representing parking spaces

💡 Hint

Think about how floors and spots are organized in a real parking lot.

A Floor contains many Spot objects, each representing a parking space on that floor.

❓ scaling

advanced

Scaling the ParkingLot system for multiple vehicle types

To support different vehicle types (car, motorcycle, truck) with different spot sizes, which class should be extended or modified?

A Extend Vehicle class to include type and size, and modify Spot to check compatibility

B Modify ParkingLot to assign spots based on vehicle type only

C Add vehicle type logic only in Floor class without changing Spot or Vehicle

D Create separate ParkingLot instances for each vehicle type

💡 Hint

Consider where vehicle size and spot size compatibility should be checked.

Vehicle class should include type and size, and Spot should verify if it can accommodate the vehicle type before parking.

❓ tradeoff

expert

Choosing the best class to track parking spot availability efficiently

For efficient tracking of available parking spots in a large parking lot, which class should maintain the availability data and why?

A Each Floor should maintain availability for its spots to reduce ParkingLot complexity

B ParkingLot should maintain a global availability map for all spots to enable quick lookup

C Each Spot should maintain its own availability and ParkingLot queries all spots directly

D Vehicle class should track availability as it knows which spots are occupied

💡 Hint

Think about balancing data centralization and query efficiency.

Having each Floor maintain availability reduces the complexity at ParkingLot level and allows faster queries per floor.

Practice

1. Which class in a parking system is responsible for managing multiple floors?

easy

A. ParkingLot

B. Floor

C. Spot

D. Vehicle

Solution

1. Step 1: Understand the role of ParkingLot

   The ParkingLot class represents the entire parking area and manages multiple floors within it.

2. Step 2: Compare with other classes

   Floor manages spots on a single level, Spot represents a single parking space, and Vehicle represents the car or bike.

3. Final Answer:

   ParkingLot -> Option A

4. Quick Check:

   ParkingLot manages floors = C [OK]

Hint: ParkingLot holds floors; floors hold spots [OK]

Common Mistakes:

• Confusing Floor as managing multiple floors
• Thinking Spot manages floors
• Assigning Vehicle to manage floors

2. Which of the following is the correct way to represent a parking spot in a class diagram?

easy

A. class Vehicle { int spotNumber; boolean isOccupied; }

B. class Spot { int spotNumber; boolean isOccupied; }

C. class Floor { int spotNumber; boolean isOccupied; }

D. class ParkingLot { int spotNumber; boolean isOccupied; }

Solution

1. Step 1: Identify the class representing a parking spot

   The Spot class should have attributes like spotNumber and isOccupied to represent a parking space.

2. Step 2: Check other classes for correctness

   Vehicle represents cars, Floor represents a level, and ParkingLot represents the whole area, so they should not have spotNumber or isOccupied attributes.

3. Final Answer:

   class Spot { int spotNumber; boolean isOccupied; } -> Option B

4. Quick Check:

   Spot class holds spot info = A [OK]

Hint: Spot class holds spot details like number and occupancy [OK]

Common Mistakes:

• Assigning spot attributes to Vehicle
• Putting spotNumber in Floor or ParkingLot
• Confusing class roles in diagram

3. Given the following code snippet, what will be the output?

class Vehicle {
  String licensePlate;
  Vehicle(String plate) { licensePlate = plate; }
}
class Spot {
  Vehicle parkedVehicle;
  boolean isOccupied() { return parkedVehicle != null; }
}
Spot spot = new Spot();
System.out.println(spot.isOccupied());

medium

A. true

B. Compilation error

C. null

D. false

Solution

1. Step 1: Analyze Spot initialization

   The Spot object is created but parkedVehicle is not assigned, so it defaults to null.

2. Step 2: Evaluate isOccupied method

   isOccupied returns true if parkedVehicle is not null; here it is null, so it returns false.

3. Final Answer:

   false -> Option D

4. Quick Check:

   parkedVehicle is null, so isOccupied() = false [OK]

Hint: Unassigned vehicle means spot is free (false) [OK]

Common Mistakes:

• Assuming default boolean is true
• Confusing null with false
• Expecting compilation error due to missing constructor

4. Identify the error in this class design snippet:

class Floor {
  List<Spot> spots;
  void addSpot(Spot s) {
    spots.add(s);
  }
}

medium

A. Spot class should be inside Floor class

B. Method addSpot should return boolean

C. spots list is not initialized before adding

D. Floor class should not have spots list

Solution

1. Step 1: Check initialization of spots list

   The spots list is declared but not initialized, so calling add on it will cause a runtime error.

2. Step 2: Validate other options

   Returning boolean is optional, Spot class can be separate, and Floor should have spots list to manage spots.

3. Final Answer:

   spots list is not initialized before adding -> Option C

4. Quick Check:

   Uninitialized list causes error = A [OK]

Hint: Always initialize lists before use [OK]

Common Mistakes:

• Ignoring list initialization
• Thinking method return type matters here
• Believing Spot must be nested class

5. You want to design a system where each Vehicle can only park in a Spot that matches its size (e.g., small, medium, large). Which class design change best supports this requirement?

hard

A. Add a size attribute to both Vehicle and Spot classes and check compatibility before parking

B. Add a size attribute only to Vehicle class and ignore Spot size

C. Add a size attribute only to Spot class and ignore Vehicle size

D. Remove size attributes and allow any Vehicle to park anywhere

Solution

1. Step 1: Understand size matching requirement

   Both Vehicle and Spot need size attributes to compare and ensure compatibility.

2. Step 2: Evaluate options

   Ignoring size in either class prevents proper matching; removing size ignores requirement.

3. Final Answer:

   Add a size attribute to both Vehicle and Spot classes and check compatibility before parking -> Option A

4. Quick Check:

   Size match needs attributes in both classes = B [OK]

Hint: Both Vehicle and Spot need size info to match [OK]

Common Mistakes:

• Adding size to only one class
• Ignoring size and allowing any parking
• Confusing attribute placement