Object-Oriented Design (OOD) practice problems are a great way to strengthen your understanding of design principles, patterns, and real-world application of OOD concepts. These problems will test your ability to think through system architectures, identify bottlenecks, and apply the right design patterns to solve problems. Here’s a list of top OOD practice problems to solve, which are commonly asked in interviews and help build your skill set.
1. Design a Parking Lot System
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Problem Description: Design a parking lot system with multiple levels, where each level can have multiple parking spaces. Each parking space can either be occupied or available. Implement the necessary classes to handle parking, ticketing, and status updates.
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Key Concepts: Inheritance, Polymorphism, State Pattern
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Challenge: How to handle multiple types of vehicles (e.g., motorcycles, compact cars, trucks) and the dynamic assignment of parking spaces. Also, think about how to manage the capacity and handle the case when the parking lot is full.
2. Design an Online Bookstore
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Problem Description: Design the system for an online bookstore, including functionality for managing books, placing orders, customer accounts, and payment processing.
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Key Concepts: Composition, Aggregation, Factory Pattern, Strategy Pattern
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Challenge: Design flexible components for order management, catalog browsing, and customer interactions. Make the system extensible to add new features (e.g., ratings, reviews).
3. Design a Social Media Feed
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Problem Description: Design the backend for a social media platform like Facebook or Instagram, focusing on the feed that displays posts from friends. Users can post text, images, and videos, and posts can have likes, comments, and shares.
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Key Concepts: Observer Pattern, Composite Pattern, Singleton Pattern
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Challenge: Ensure that the feed updates efficiently when a new post is added. Also, handle user preferences for what content to show, such as filtering out unwanted posts.
4. Design a Library Management System
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Problem Description: Create a system for managing books in a library. Users can borrow, return, or reserve books. Admins can add or remove books from the catalog, and keep track of due dates and fines.
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Key Concepts: Inheritance, Composite Pattern, Observer Pattern
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Challenge: Think about handling different types of users (e.g., students, faculty, visitors) and the rules for borrowing books, such as maximum checkout duration and penalties for late returns.
5. Design a Notification System
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Problem Description: Build a notification system that can send different types of notifications (e.g., SMS, email, push notifications) to users based on events or alerts. Users should be able to set preferences for notification types.
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Key Concepts: Strategy Pattern, Observer Pattern, Factory Pattern
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Challenge: Handle asynchronous events, and implement a system that can scale to accommodate thousands or even millions of users. Make it possible for users to opt-in or opt-out of specific types of notifications.
6. Design a Ride-sharing Service
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Problem Description: Design a system like Uber or Lyft that matches riders with drivers based on proximity. It should handle trip requests, payments, ratings, and driver availability.
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Key Concepts: State Pattern, Strategy Pattern, Factory Pattern
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Challenge: Handle the dynamic nature of ride requests, implement surge pricing, and create a reliable matching algorithm for rider and driver availability.
7. Design a Chess Game
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Problem Description: Implement a system that allows players to play chess. The system should support board setup, move validation, and check/checkmate detection.
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Key Concepts: Command Pattern, State Pattern, Composite Pattern
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Challenge: Ensure that the system can track the state of the game accurately and validate moves for each piece. Consider adding advanced features like undo/redo functionality and multiplayer support.
8. Design a File System
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Problem Description: Design a simple file system to handle directories, files, and subdirectories. It should support operations like adding, deleting, and moving files and directories.
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Key Concepts: Composite Pattern, Visitor Pattern, Singleton Pattern
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Challenge: Design for scalability, where large numbers of files and directories can be handled efficiently. Also, think about the structure of file metadata, such as file sizes, permissions, and timestamps.
9. Design a Movie Ticket Booking System
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Problem Description: Create a system that allows users to search for movies, book tickets, choose seats, and make payments. Admins should be able to add or remove movies and showtimes.
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Key Concepts: Factory Pattern, Strategy Pattern, Observer Pattern
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Challenge: Handle different types of seats (VIP, regular), manage availability in real time, and provide a way to issue refunds in case of cancellations.
10. Design a Cloud Storage System
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Problem Description: Design a cloud storage system like Dropbox or Google Drive that allows users to upload, download, and organize files. It should support file versioning, sharing, and file access permissions.
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Key Concepts: Composite Pattern, Singleton Pattern, Strategy Pattern
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Challenge: Handle large files, file versioning, and user access control. Ensure the system can scale to support millions of users and files.
11. Design a Stock Trading System
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Problem Description: Build a system for buying and selling stocks, including real-time price updates, order matching, and transaction processing.
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Key Concepts: Observer Pattern, Factory Pattern, State Pattern
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Challenge: Implement order types like market orders, limit orders, and stop orders, and handle large volumes of trades efficiently.
12. Design a Payment Gateway
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Problem Description: Implement a system that processes payments, including handling credit card information, payment authorization, and transaction history.
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Key Concepts: Adapter Pattern, Strategy Pattern, Singleton Pattern
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Challenge: Ensure the system can integrate with different payment processors, handle fraud detection, and provide a seamless user experience for both customers and merchants.
13. Design an E-commerce Checkout System
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Problem Description: Create an e-commerce checkout system where users can select products, apply discount codes, and complete the payment process.
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Key Concepts: Composite Pattern, Strategy Pattern, Factory Pattern
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Challenge: Handle product catalog, cart management, dynamic pricing, and support for different payment methods.
14. Design a Customer Support Ticket System
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Problem Description: Implement a system for managing customer support tickets, where users can submit tickets, and agents can track, respond to, and close tickets.
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Key Concepts: Observer Pattern, State Pattern, Command Pattern
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Challenge: Design for scalability and ensure that tickets are routed efficiently to the appropriate agents. Consider adding support for automated ticket triage using AI.
15. Design an ATM System
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Problem Description: Design a system to simulate ATM operations, including account balance management, withdrawals, deposits, and transaction history.
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Key Concepts: State Pattern, Factory Pattern, Singleton Pattern
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Challenge: Handle multiple types of transactions securely and ensure the system can work with different types of accounts (e.g., checking, savings).
These practice problems cover a wide range of common OOD topics and patterns, such as design patterns, inheritance, polymorphism, and system architecture. Solving these problems will prepare you for real-world system design challenges and make you confident in OOD interviews.