Description

Editorial

Design a Car Rental System

Intermediate

Design an object-oriented car rental system that manages a fleet of vehicles across multiple branches. Customers can search for vehicles, make reservations (including one-way rentals), pick up and return cars, with pricing determined by a pluggable strategy.

The system models a vehicle hierarchy (Sedan, SUV, Luxury), reservation lifecycle (pending → confirmed → active → completed), branch-based fleet management, and swappable pricing strategies (default, weekend surcharge, loyalty discount).

Core Use Cases

Browse available vehicles

Search for vehicles by type, branch, and availability dates

Make a reservation

Reserve a specific vehicle for a date range with pickup and drop-off branches

Cancel a reservation

Cancel a pending or confirmed reservation and release the vehicle

Pick up vehicle

Mark the reservation as active when the customer collects the car

Return vehicle

Complete the rental, calculate the final cost (including late fees), and update vehicle status

One-way rental

Pick up at one branch and drop off at a different branch

Dynamic pricing

Apply different pricing strategies (default, weekend surcharge, loyalty discount)

Manage fleet

Add/remove vehicles and branches; mark vehicles for maintenance

Constraints

A vehicle can only be in one reservation at a time for overlapping dates
A reservation transitions through PENDING → CONFIRMED → ACTIVE → COMPLETED (or CANCELLED)
Drop-off branch can differ from pickup branch (one-way rental)
Late returns incur additional charges based on the daily rate
Only one pricing strategy is active at a time, but it can be swapped at runtime

Assumptions

In-memory storage (no database persistence)
Single-threaded access (thread-safety is a follow-up)
No insurance or add-on packages (follow-up topic)
Unlimited fleet — no waitlist for unavailable vehicle types

In Scope

Vehicle hierarchy (Sedan, SUV, Luxury)
Branch/location management with fleet
Reservation lifecycle (create, confirm, pickup, return, cancel)
Pricing strategy abstraction
One-way rentals between branches
Customer registration and rental history

Out of Scope

Payment processing / gateway integration
Insurance and damage claims
GPS tracking of vehicles
Waiting list when no vehicles available
Multi-currency pricing

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

UML

Code

Submissions

Solutions

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

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Description

Editorial

Design a Car Rental System

Intermediate

Core Use Cases

Browse available vehicles

Search for vehicles by type, branch, and availability dates

Make a reservation

Reserve a specific vehicle for a date range with pickup and drop-off branches

Cancel a reservation

Cancel a pending or confirmed reservation and release the vehicle

Pick up vehicle

Mark the reservation as active when the customer collects the car

Return vehicle

Complete the rental, calculate the final cost (including late fees), and update vehicle status

One-way rental

Pick up at one branch and drop off at a different branch

Dynamic pricing

Apply different pricing strategies (default, weekend surcharge, loyalty discount)

Manage fleet

Add/remove vehicles and branches; mark vehicles for maintenance

Constraints

A vehicle can only be in one reservation at a time for overlapping dates
A reservation transitions through PENDING → CONFIRMED → ACTIVE → COMPLETED (or CANCELLED)
Drop-off branch can differ from pickup branch (one-way rental)
Late returns incur additional charges based on the daily rate
Only one pricing strategy is active at a time, but it can be swapped at runtime

Assumptions

In-memory storage (no database persistence)
Single-threaded access (thread-safety is a follow-up)
No insurance or add-on packages (follow-up topic)
Unlimited fleet — no waitlist for unavailable vehicle types

In Scope

Vehicle hierarchy (Sedan, SUV, Luxury)
Branch/location management with fleet
Reservation lifecycle (create, confirm, pickup, return, cancel)
Pricing strategy abstraction
One-way rentals between branches
Customer registration and rental history

Out of Scope

Payment processing / gateway integration
Insurance and damage claims
GPS tracking of vehicles
Waiting list when no vehicles available
Multi-currency pricing

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

UML

Code

Submissions

Solutions

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

Loading canvas...

Design a Car Rental System - Low-Level Design | OneNoughtOne

Design a Car Rental System

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you prevent double-booking during concurrent reservation attempts?

2How would you add insurance and add-on packages (GPS, child seat)?

3How would you implement a waitlist when no vehicles of the requested type are available?

4How would you handle surge/seasonal pricing?

Key Topics

Asked At

Design a Car Rental System

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you prevent double-booking during concurrent reservation attempts?

2How would you add insurance and add-on packages (GPS, child seat)?

3How would you implement a waitlist when no vehicles of the requested type are available?

4How would you handle surge/seasonal pricing?

Key Topics

Asked At