55 Low-Level Design Interview Questions With Example Answers

By Indeed Editorial Team

Published 27 July 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

As an important part of system design, low-level design (LLD) converts high-level design into ready-to-code components. It is now common to have an LLD round during a tech interview. Knowing what kind of questions you may face as a software developer can help you prepare suitable answers and feel more confident during the interview. In this article, we discuss 55 low-level design interview questions and some sample answers for your reference.

General Low-Level Design Interview Questions

Here are 10 general low-level design interview questions the interviewer might ask:

  1. Why did you become a software designer/developer?

  2. What are your favourite software development tools?

  3. Which aspects of low-level design do you find the most interesting and challenging?

  4. How comfortable are you reviewing others' code?

  5. How much do you code each day?

  6. How do you explain technical information to non-technical audiences?

  7. What aspects of this position interest you most?

  8. How do you stay updated on industry developments?

  9. What qualities software engineers require to have?

  10. What do you consider the key principles of software designing?

Related: How To Prepare For A Job Interview?

Questions About Experience And Background

Here are 12 questions you may encounter regarding specific details in your work history and educational qualifications:

  1. Tell me about your background in software development.

  2. Outline your experience in system design.

  3. Which object-oriented languages do you know?

  4. Which technologies do you have experience using in your past roles?

  5. What is your process for reviewing code that another person wrote?

  6. Tell me about a recent project you worked on.

  7. Which design patterns do you use most often?

  8. Describe an object-oriented system you designed successfully.

  9. Describe a difficult bug you fixed in a large application.

  10. How do you ensure quality and fix errors?

  11. What were your responsibilities in your previous position?

  12. What project management tools are most useful in your role as a software engineer/developer?

Related: How To Crack A Job Interview?

In-Depth Questions For Low-Level Design

Here are 29 questions the interviewer may ask to evaluate your skill level:

  1. Which object-oriented principles do you think are most important in low-level design?

  2. Elaborate on the YAGNI and DRY principles.

  3. What are UML diagrams and how are they classified?

  4. What are design patterns? What is the main benefit of using them?

  5. How are design patterns classified?

  6. Elaborate on some of the common criticisms against design patterns.

  7. How to prevent singleton pattern from reflection, serialisation and cloning?

  8. Design a web crawler system or search engine.

  9. Design a traffic control system.

  10. Design a snake and ladder game using low-level design.

  11. Design a parking lot using object-oriented principles.

  12. Design data structures and algorithms for an in-memory file system.

  13. Design a global file sharing and storage app.

  14. Design a movie ticket booking system.

  15. Design an e-commerce website that uses microservices to handle transactions.

  16. Design a URL Shortening service.

  17. Design a chess game.

  18. Design a feed posting system on a social media application.

  19. Design a mobile chat application.

  20. Design a food delivery system.

  21. Design a limit order book for trading systems.

  22. Design a job portal like Indeed.

  23. Design a global ride-hailing service.

  24. Design a room booking and renting application.

  25. Design an elevator system.

  26. Design an ATM.

  27. Design a global video streaming service.

  28. Design an autocomplete feature like word suggestions on search engines and scale it to millions of users.

  29. Design the vending machine in Java.

Related: 23 Interview Tips: How To Get The Job

Low-Level Design Interview Questions With Sample Answers

Here are some questions with strategic answers you can provide in your next LLD interview:

1. Tell me about some of the code writing best practices for low-level design.

With a complex code, there are higher chances of vulnerability to errors. Certain code quality standards, if implemented, reduce the risk of potential errors and project failures. Interviewers may like to test your knowledge about coding standards in the development of software programs. Emphasise the importance of structure, readability and cleanliness in your answer.

Example: "While writing code for LLD, it is necessary to write well-structured code while following clean coding practices for classes and methods. It is important that instead of trying to fit design patterns into the code forcefully, we check if it is possible to naturally solve a given problem using any available design pattern. Another best practice of writing code is to make it simple and readable, as complex code is prone to errors."

Related: 40 Design Pattern Interview Questions (With Example Answers)

2. What do you know about the SOLID principles?

SOLID principles are a coding standard that is necessary for all developers to know before developing software. These principles help avoid pitfalls that lead to bad software design. They are popular across the object-oriented design spectrum and, as a software engineer or developer, the interviewer expects you to know these principles well. Outline the names of the principles and its overall utility in your answer. You can go into more detail if the interviewer asks any follow-up questions.

Example: "The SOLID principles, popularised by Robert C. Martin, are a set of five principles that include the Single responsibility principle, the Open-closed principle, the Liskov substitution principle, the Interface segregation principle and the Dependency inversion principle. These principles handle complicated design patterns and reduce dependencies so that engineers can alter one area of software without affecting others. It makes the code more logical, extendable and read."

Related: 30 System Design Interview Questions (With Example Answers)

3. Walk me through your process of solving a standard LLD problem.

Before getting into a hands-on LLD design question, the interviewer may like to know about your approach to solving these types of practical questions. Outline the steps you are likely to take and elaborate on your method for each step. When answered correctly, this question can signal to the interviewer that you have a clear understanding of solving LLD problems and know how to set your priorities right.

Example: "In the process of solving a standard LLD problem, my first step is to clarify the question and gather the necessary requirements. I do this by asking relevant questions regarding the problem, which helps me understand more about the system behaviour, attributes and expected features.

Next, I create the class diagram, use-case diagram and schema diagram, as required. To do so, I define the core classes and objects, how the different classes interact with each other, actors who interact with the system and the use cases for each actor. I also define the relations between classes by observing the interactions between them. After structuring my thoughts properly, I begin to write the code. In this process, I apply the design patterns, object-oriented principles and SOLID principles wherever possible, to make the system reusable, extensible and maintainable."

Related: 50 Software Engineer Interview Questions (With Answers)

4. What do you think is the goal of efficient low-level design?

As low-level design questions are intentionally unstructured and open-ended, the interviewer may want to make sure that you are aware of the ultimate aim of LLD before writing the code. In your answer, demonstrate that you understand how to create elegant, maintainable object-oriented code. Your answer would suggest your understanding of LLD and its end goals.

Example: "Through efficient low-level design, software developers aim to build modular, extensible, reusable and maintainable software from a set of requirements. The primary goal of effective low-level design is to maintain and extend the software easily, as that takes the maximum effort in the software development life cycle. Efficient LLD directly contributes to the maintainability and extensibility of software."

Related: 30 Interview Questions For Software Developers (With Answers)

Interview Tips For Low-Level Design

Here are some tips to help you succeed in an LLD interview:

  • Make sure you fully understand the question. Read the question thoroughly and listen to the interviewer with full attention. Avoid making assumptions and jumping to conclusions.

  • List the requirements first. This can provide a clear reference for what to do next in the designing process. After listing all the requirements, they become the base for design and help you proceed step by step accordingly.

  • Take your time instead of making a mistake in a time crunch. Given the 40-45 minutes provided for a question, you may realise that this is not enough time to design and code for all the requirements. Hence consult the interviewer and discuss the core requirements that you want to consider for the design.

  • Do a little more than asked. If you have time, try to write the test cases for the code and handle all the exceptions, even if the interviewer does not ask for it. It can give you an edge over other candidates.

  • Discuss your answer with the interviewer. While formulating your approach to the question and constructing your answer, explain each step to the interviewer so they can give you hints and correct you if they want. But avoid asking for help directly.

  • Practice the common questions. Solving popular low-level design questions can improve your weaknesses, boost your confidence and help you develop a thought process for solving any problem. You may even get some questions common in your real interview which you previously practiced.

  • Learn to use the necessary tools. Get comfortable using whiteboard apps and code editors beforehand, so you do not waste any time in the real interview figuring out how things work.

  • Remember that there are no right or wrong answers. It is only necessary to come up with a good design within a limited time. You can be confident in your design if you start designing from the basic entity in your system and then iteratively proceed towards the higher components.

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