System Design - Parking Lot

System Design Interview Question: DESIGN A PARKING LOT - asked at Google, Facebook

1. System Design

2. Algorithmic Problem Solution

3. Object Oriented Design Question Problem Statement - Design a parking lot, Wants a system to manage thousands of cars.

4. Handling Ambiguity - recognize the breadth of the question

5. Clarify question like

   • do you want a system design

   • do you want class hierarchy

6. Systematic Approach (take a step back and don't rush)

   • How is the parking lot designed?

     • Building

     • Open space

     • Assessibility

   • How many spots

     • 10 spots

     • 1000 spots multiple buildings

   • Multiple levels?

     • depedencies

     • optimize to fill up certain areas first

   • Multiple entrances

     • Concurrency issue

     • race condition (When system tries to access same spot at same time)

   • Pricing strategy

     • Premium

     • Fair pricing strategy if the required size parking spot not available

     • Parking spot for disability (near to entrance)

     • Economical parking spot

     • Dynamic pricing (Higher pricing at high rush hour)

Design a system for 4 sizes -

1. Small (motorcycle)

2. Medium (car)

3. Large (Bus)

4. Extra Large (Truck) Assumption

5. Can put small car to bigger spot Class Hierarchy -

Abstract Vehicle

• String licensePlate

• enum color Implementation of vehicle (Create 4 classes that inherit from the vehicle)

• MotorCycle (S)

• Car (M)

• Bus (L)

• Truck (XL) class ParkingLot ( zipCode:int )

placeVehicle ( vehicle:Vehicle )

return Spot class Spot ( id:Long, size:enum ) Database for storing spots, vehicles etc. Find free spot (can have an array of spot, but it will be a linear operation to find a free spot)

We can create a stack which have free spots. 4 stacks, each for storing free spots of each size. placeVehicle - O(1), constant time operation + put in HashMap (Fast Lookup) Spot : removeVehicle ( vehicle : Vehicle )

Look up Hashmap