Design Parking System

Design Parking System

What is this problem about?

The Design Parking System coding problem is a great introductory design task. You need to create a class that manages parking spaces for three types of cars: big, medium, and small. The system is initialized with a fixed number of slots for each size. You then implement an addCar method that checks if a slot of the appropriate type is available and "occupies" it if possible.

Why is this asked in interviews?

Companies like Uber and Amazon use this "Easy" question to screen for basic object-oriented programming (OOP) skills. It tests whether you can represent real-world constraints using simple variables and whether you can write clean, readable code. It's also a test of your ability to follow instructions precisely and handle basic state modification.

Algorithmic pattern used

The Simulation design pattern or Counting interview pattern is used here. You simply maintain three integer counters (or an array of size 3). When a car arrives, you check if the corresponding counter is greater than zero. If it is, you decrement the counter and return true; otherwise, return false.

Example explanation

Initialize: big=1, medium=1, small=0.

1. addCar(big): 1 slot available. Decrement big to 0. Returns true.
2. addCar(big): 0 slots available. Returns false.
3. addCar(medium): 1 slot available. Decrement medium to 0. Returns true.
4. addCar(small): 0 slots available. Returns false.

Common mistakes candidates make

• Over-engineering: Using complex hash maps or queues for a problem that only requires three integers.
• Concurrency: In a real-world scenario, you'd need to consider thread-safety, though it's usually not required for this specific coding problem unless specified.
• Parameter Mapping: Forgetting that the input for car types is typically 1, 2, and 3, which needs to be mapped to the correct internal variables.

Interview preparation tip

For "Easy" design problems, focus on readability. Use a simple array where the index corresponds to the car type (adjusted for 0-indexing) to make your code more concise and professional.