██FR█████ █INTELL███████████

How do I prepare for low level system design?


This content originally appeared on DEV Community and was authored by Muhammad Salem

Preparing for low-level system design interviews requires a structured approach to mastering object-oriented design (OOD) and software design principles. Here is a comprehensive guide to help you prepare effectively:

1. Understand the Basics of OOD

  • Object-Oriented Principles: Learn the four main principles of OOD:
    • Encapsulation: Keeping the data (attributes) and the code (methods) that manipulates the data together.
    • Abstraction: Hiding complex implementation details and showing only the necessary features of an object.
    • Inheritance: Mechanism to create a new class using the properties and methods of an existing class.
    • Polymorphism: Ability of different classes to be treated as instances of the same class through inheritance.

2. Learn SOLID Principles

  • Single Responsibility Principle (SRP): A class should have one and only one reason to change.
  • Open/Closed Principle (OCP): Classes should be open for extension but closed for modification.
  • Liskov Substitution Principle (LSP): Objects of a superclass should be replaceable with objects of a subclass without affecting the functionality.
  • Interface Segregation Principle (ISP): Many client-specific interfaces are better than one general-purpose interface.
  • Dependency Inversion Principle (DIP): Depend on abstractions, not on concretions.

3. Study Common Design Patterns

  • Creational Patterns: Singleton, Factory, Abstract Factory.
  • Structural Patterns: Adapter, Facade, Decorator.
  • Behavioral Patterns: Strategy, Observer.
  • Resources: “Head First Design Patterns” by Eric Freeman and Elisabeth Robson.

4. Practice Common System Design Problems

  • Design a Parking Lot
  • Design a Library Management System
  • Design an Online Bookstore
  • Design a Social Media Platform
  • Design a Chess Game

5. Brush Up on UML Diagrams

  • Class Diagrams: Represent classes and their relationships.
  • Sequence Diagrams: Show how objects interact in a particular sequence.
  • Use Case Diagrams: Illustrate system functionalities and user interactions.
  • Activity Diagrams: Represent workflows of stepwise activities.

6. Implement Small Projects

  • Create small projects that require careful design:
    • Inventory Management System
    • Employee Management System
    • E-commerce Application
  • Focus on how you structure your classes, relationships, and interactions between components.

7. Code Reviews and Refactoring

  • Regularly review and refactor your code.
  • Learn to identify code smells and apply refactoring techniques.
  • Resources: “Refactoring: Improving the Design of Existing Code” by Martin Fowler.

8. Mock Interviews and Practice

  • Participate in mock interviews with peers or mentors.
  • Use platforms like Pramp, Interviewing.io, or LeetCode Discuss to practice system design problems.
  • Record your solutions and get feedback to improve.

9. Study Real-World Systems

  • Analyze the design of popular open-source projects on GitHub.
  • Read engineering blogs and case studies from tech companies.

10. Review and Revise

  • Regularly review your notes and solutions.
  • Stay updated with new design patterns and architectural styles.

Sample Problem Walkthrough: Design a Parking Lot

Step 1: Gather Requirements

  • Different types of parking spots: regular, compact, handicapped.
  • Payment methods and fee calculation.
  • Entry and exit points.
  • Tracking available spots.

Step 2: Identify Main Components

  • ParkingLot: Manages parking spots, entry, and exit.
  • ParkingSpot: Represents a single parking spot.
  • Vehicle: Base class for vehicles.
  • Ticket: Manages parking tickets.
  • Payment: Handles payment processing.

Step 3: Define Classes and Relationships 

class ParkingLot {
    List<ParkingSpot> spots;
    Map<String, Ticket> activeTickets;

    Ticket parkVehicle(Vehicle vehicle);
    void exitVehicle(Ticket ticket);
}

class ParkingSpot {
    String spotId;
    boolean isOccupied;
    Vehicle currentVehicle;
    SpotType spotType; // Enum for regular, compact, handicapped

    boolean assignVehicle(Vehicle vehicle);
    void removeVehicle();
}

class Vehicle {
    String licensePlate;
    VehicleType vehicleType; // Enum for car, truck, bike
}

class Ticket {
    String ticketId;
    Date entryTime;
    Date exitTime;
    Vehicle vehicle;
    double calculateFee();
}

class Payment {
    String ticketId;
    double amount;
    boolean processPayment();
}

Step 4: Design UML Diagram

  • Create class and sequence diagrams to visualize the interaction and design.

Step 5: Implement and Test

  • Write unit tests for each class.
  • Simulate parking, exiting, and payment scenarios.

By following this structured approach and continually practicing, you can effectively prepare for low-level system design interviews and improve your ability to design robust software systems.

To get the most value from practicing low-level design problems, especially with a resource like “Grokking the Object-Oriented Design Interview,” you should follow a methodical approach. Here are tips and tricks for effective low-level design practices:

1. Understand the Problem Thoroughly

  • Clarify Requirements: Before diving into the solution, ensure you understand the problem statement and clarify any ambiguities.
  • Identify Key Features: Break down the problem into essential features and functionalities.

2. Break Down the Design

  • Modular Design: Divide the problem into smaller, manageable modules or components.
  • Single Responsibility Principle: Ensure each class or module has a single responsibility or purpose.

3. Use Design Patterns Wisely

  • Appropriate Patterns: Identify and apply suitable design patterns for each component. For example, use the Singleton pattern for managing a single instance of a class.
  • Pattern Combinations: Sometimes, combining multiple patterns can lead to an optimal solution.

4. Think Through Edge Cases

  • Robust Design: Consider edge cases and how your design will handle them. This includes error handling, boundary conditions, and performance considerations.
  • Scalability and Extensibility: Design with scalability in mind, allowing for easy extension or modification.

5. Visualize with UML

  • Class Diagrams: Create class diagrams to visualize the relationships between different components.
  • Sequence Diagrams: Use sequence diagrams to understand object interactions over time.
  • Use Case Diagrams: Map out user interactions and system functionalities.

6. Implement and Test

  • Write Clean Code: Follow best practices for clean and maintainable code. Use meaningful names, consistent formatting, and document your code.
  • Unit Testing: Write unit tests for each class and component. Test both typical and edge cases.
  • Refactor: Continually improve your design and code. Refactor for better performance, readability, and maintainability.

7. Review Solutions Critically

  • Analyze Sample Solutions: Study the solutions provided in your resource. Understand why certain design choices were made and how they address the problem requirements.
  • Compare and Contrast: Compare your solution with the sample. Identify areas of improvement or alternative approaches.
  • Feedback Loop: Seek feedback from peers, mentors, or online forums. Use constructive criticism to refine your design skills.

8. Practice Regularly and Variedly

  • Diverse Problems: Practice a variety of design problems. Each problem will help you understand different aspects of OOD.
  • Consistency: Set a regular practice schedule. Consistent practice will reinforce concepts and improve your skills.
  • Time Yourself: Simulate interview conditions by timing your design process. This helps improve your efficiency and ability to think under pressure.

9. Document Your Process

  • Design Journal: Keep a journal of your design problems, solutions, and learnings. Document the steps you took, the design patterns used, and any challenges faced.
  • Reflect and Iterate: Periodically review your journal to reflect on your progress. Identify patterns in your mistakes and areas where you can improve.

10. Build Projects

  • Real-World Applications: Apply your design skills to small projects or contribute to open-source projects. This gives practical experience and reinforces your learning.
  • Incremental Complexity: Start with simple projects and gradually take on more complex systems. This builds confidence and competence.

Sample Approach Using Grokking OOD Problems

  1. Read and Analyze: Carefully read the problem statement and break it down into core requirements.
  2. Plan: Sketch a high-level design and decide on the classes, interfaces, and relationships.
  3. Detail Design: Flesh out the details of each component, considering design principles and patterns.
  4. Code: Implement the design in code, adhering to clean coding standards.
  5. Test: Write tests to ensure your implementation meets the requirements and handles edge cases.
  6. Review: Compare your solution with the provided solution, noting differences and improvements.
  7. Refine: Refactor your design and code based on insights gained from the review.

Example Problem Walkthrough: Design a Library Management System

Step 1: Clarify Requirements

  • Core Features: Book catalog, member management, borrowing and returning books, fee calculation.
  • Key Entities: Books, Members, Librarians, Borrowing Records.

Step 2: Identify Classes and Responsibilities

  • Book: Title, Author, ISBN, Status (available, borrowed).
  • Member: Member ID, Name, Contact Details, Borrowing Limit.
  • Librarian: Manage books, Assist members.
  • BorrowingRecord: Book, Member, Borrow Date, Return Date, Fee.

Step 3: Apply Design Patterns

  • Factory Pattern: For creating instances of Books, Members.
  • Observer Pattern: To notify members of due dates.
  • Singleton Pattern: For a single instance of Library.

Step 4: Create UML Diagrams

  • Draw class and sequence diagrams to visualize the structure and interactions.

Step 5: Implement and Test

  • Code the classes and write unit tests to validate the functionality.

Step 6: Review and Refine

  • Compare with the solution from Grokking OOD, identify improvements, and refine your design.

By following these steps and continually practicing, you will develop strong low-level design skills and be well-prepared for your interviews.


This content originally appeared on DEV Community and was authored by Muhammad Salem