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Table of contents
1.
Introduction
2.
Most Asked Low-Level Design Interview Questions
2.1.
1. What do you understand by low-level design?
2.2.
2. How can you solve an LLD problem?
2.3.
3. What are the advantages of a low-level design?
2.4.
4. What is Object-Oriented Language?
2.5.
5. Why do we use Object-Oriented Language?
2.6.
6. Elaborate on the YAGNI principle.
2.7.
7. Elaborate on the DRY principle.
2.8.
8. What is UML?
2.9.
9. What are design patterns?
2.10.
10. What is the main benefit of using design patterns?
2.11.
11. How are design patterns classified?
2.12.
12. What are the most popular design patterns?
2.13.
13. What is the single responsibility principle?
2.14.
14. What is multithreading?
2.15.
15. Explain the advantages of using SOLID Principles.
2.16.
16. How do you design the Vending Machine?
2.17.
17. How do you design a traffic control system?
2.18.
18. How would you create your own Instagram?
2.19.
19. How do you design a chat application like WhatsApp or Facebook Messenger?
2.20.
20. How to design an ATM machine?
2.21.
21. What is the difference between a sequence diagram and an activity diagram?
2.22.
22. What does Strategy Pattern mean?
2.23.
23. What is your process for reviewing code that another person wrote?
2.24.
24. Which technologies do you have experience using in your past roles?
2.25.
25. Tell me about a recent project you worked on.
2.26.
26. Describe an object-oriented system you designed successfully.
2.27.
27. Describe a difficult bug you fixed in a large application.
2.28.
28. What were your responsibilities in your previous position?
2.29.
29. Which low-level design aspects do you find the most interesting and challenging?
2.30.
30. How do you ensure quality and fix errors?
3.
Conclusion
Last Updated: Jun 20, 2024

Low Level Design Interview Questions

Author Vikash Kumar
0 upvote
Master Python: Predicting weather forecasts
Speaker
Ashwin Goyal
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Introduction

Low-Level Design, abbreviated as LLD, is about giving details to High-Level Design.

It includes a detailed description of every module, class, and interface. The purpose of an LLD is to provide the internal logical design of the actual computer code. LLD defines class diagrams with methods and relationships between classes and program specifications. It specifies the modules in detail so that the programmer can code the program directly from the text.

Low-Level Design interview questions

This article will discuss some of the top Low-Level Design interview questions with their proper answers. This article will help you brush up on your concepts of Low-Level Designing and prepare for your interviews.
 

Most Asked Low-Level Design Interview Questions


Here, we are going to discuss most asked Low-Level Design interview questions.

1. What do you understand by low-level design?

Ans: Low-level design is a detailed and technical process of creating specific blueprints for a software system's components and modules focused on implementing the requirements outlined in the system's architecture.


2. How can you solve an LLD problem?

Ans: To solve an LLD problem, one should gather requirements and avoid making assumptions. One should create the class, use case diagrams, and write code using design patterns, object-oriented principles, and SOLID principles. This will help ensure the program's efficiency, reusability, and easy maintenance.


3. What are the advantages of a low-level design?

Ans: LLD has several advantages, including providing a logical design to program code and creating class diagrams with relations. It also includes program specifications, breaking down modules for easy coding, developing software with minimal debugging and testing, and reducing costs and maintenance.


4. What is Object-Oriented Language?

Ans: Object-oriented language is a programming language designed to model real-world entities and concepts using objects containing data and code to interact with other objects. OOP concepts such as encapsulation, inheritance, and polymorphism enable modular, scalable, and reusable software development.


5. Why do we use Object-Oriented Language?

Ans: Object-oriented language offers several advantages, including saved development time, higher productivity, ease of breaking programs down into more minor problems, better software quality, reduced maintenance costs, and easy upgrading to larger systems. It also enables secure programming, eliminating redundant code, more straightforward interface descriptions, and more detailed modeling through data-centered design.


6. Elaborate on the YAGNI principle.

Ans: The YAGNI software development principle stands for "You Ain't Gonna Need It." It suggests that a programmer should only add necessary software functionality, even if it seems to be needed in the future. In other words, keep the software design simple and add features as needed rather than creating complex and potentially unnecessary code that may be difficult to maintain or modify.


7. Elaborate on the DRY principle.

Ans: The DRY is a software development principle that stands for "Don't Repeat Yourself". It emphasizes the importance of reusing code. It suggests that programmers avoid duplicating code and instead create a single, reusable source of truth that can be used throughout a program or project.


8. What is UML?

Ans: UML (Unified Modeling Language) is a standardized visual modeling language. We use it to design, visualize, and document software systems. UML provides a set of graphical notations and techniques to create visual models of software systems. This is used to understand, communicate, and validate system structure and behavior.


9. What are design patterns?

Ans: Design patterns are reusable solutions to common problems that arise during the software design process. They are tried and tested solutions. They improve the quality, maintainability, and reusability of software while also streamlining the design process.


10. What is the main benefit of using design patterns?

Ans: The main benefit of using design patterns is that they provide a proven and reusable solution to common software design problems. By using design patterns, developers can avoid having to solve problems from scratch and instead can leverage the expertise and experience of others. This can save time and effort and reduce the risk of errors and bugs. It improves software quality, maintainability, and reusability.

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11. How are design patterns classified?

Ans: Design patterns are classified into three categories:

  • Creational Patterns: They deal with object creation mechanisms, trying to create objects properly for the situation.
  • Structural Patterns: They deal with object composition and how classes and objects are combined to form larger structures.
  • Behavioral Patterns: They deal with communication between objects, focusing on how objects interact and fulfill their responsibilities within the more extensive system.


12. What are the most popular design patterns?

Ans: Several design patterns are used widely in software development. Some of them are:

  • Singleton Pattern: Ensures that only one class instance is created and provides a global point of access to that instance.
  • Factory Pattern: Provides a way to create objects without specifying the exact class of object that will be made.
  • Adapter Pattern: It converts the interface of a class into another interface that clients expect.
  • Decorator Pattern: Dynamically adds behaviors to an object without changing its interface.


13. What is the single responsibility principle?

Ans: The Single Responsibility Principle (SRP) is a design principle that states that a class or module should have only one responsibility or job. This makes the code easier to understand, test, and maintain. It also improves its modularity, extensibility, and reusability.


14. What is multithreading?

Ans: Multithreading allows multiple threads to run concurrently within a single process, improving performance and resource utilization. Threads can perform specific tasks and communicate with each other. It helps to handle challenges such as synchronization and race conditions.


15. Explain the advantages of using SOLID Principles.

Ans: The SOLID principles are five design principles for writing clean and maintainable code.

  • Modularity: SOLID principles promote modularity and encapsulation, which makes it easier to maintain and update code over time.
  • Scalability: By reducing the coupling between different parts of the code, SOLID principles make it easier to scale applications as they grow.
  • Testability: SOLID principles encourage writing code that is easier to test, as it is broken down into smaller, more manageable pieces.
  • Flexibility: SOLID principles promote flexible code that can quickly adapt to changing requirements and business needs.
  • Reusability: SOLID principles promote the creation of reusable code in other parts of an application or other applications.


16. How do you design the Vending Machine?

Ans: We are designing and implementing a vending machine that keeps track of inventory, accepts cash, and dispenses items. The machine must confirm the cash input with the selected item's price and display an error message in case of insufficient money or an unavailable item. The design approach involves identifying the actors and actions performed by them. And defining different states of the machine and implementing a State Design Pattern to abstract state-related behavior into separate classes. The code implementation using the pattern is reusable, extensible, readable, and clean.


17. How do you design a traffic control system?

Ans: I will design a traffic control system using the following steps:

  • Analyze traffic and pedestrian volume.
  • Determine traffic flow and crossing times.
  • Calculate vehicle clearing time to program timer.
  • Set signal change intervals of 20-30 seconds.
  • Strategically place traffic lights for visibility to motorists and pedestrians.


18. How would you create your own Instagram?

Ans: For my own Instagram, I would start with user authentication, requiring users to register an account and log in to access the app. Each user would have a profile where they can edit their details. The news feed would be the main page that displays users' posts and those they follow. Users can post photos, videos, and text, follow other users, like and comment on posts, and send and receive direct messages. Additionally, a search feature would be available to search for other users, posts, and hashtags. Hashtags can be added to posts and used for searching. Finally, users will receive notifications for new followers, likes, comments, and direct messages.


19. How do you design a chat application like WhatsApp or Facebook Messenger?

Ans: To design a chat application like Facebook or Whatsapp, I would follow these steps:

  • First, set the basic requirements for the chat application, such as user registration, messaging, and notifications.
  • Then I will design the database schema to store user information and messages.
  • After that, I will design the user interface for the chat application. It includes features like message threads, media sharing, and group chats.
  • The next step is providing security features like end-to-end encryption to ensure the privacy and security of user data.
  • Finally, I need to integrate the chat application with third-party services like cloud storage for media and push notification services for alerts.


20. How to design an ATM machine?

Ans: For designing an ATM, one should follow the given steps:

  • User Authentication: Users need to authenticate themselves by providing a PIN associated with their account.
  • Main Menu: After successful authentication, the main menu is presented to the users with multiple options.
  • Withdrawal: This is the functionality to withdraw cash. The machine checks and confirms information to give a successful withdrawal.
  • Deposit: This feature allows a user to add cash to their bank 
  • Transaction Receipt: It will provide details of the transaction.
  • Error Handling: If an error occurs during a transaction, such as a card jam or a failure to dispense cash, the ATM will display an error message and prompt the user to try again or contact customer support.


21. What is the difference between a sequence diagram and an activity diagram?

Ans: 

  • Sequence diagrams focus on the interactions between objects or components, while activity diagrams focus on the flow of activities or actions in a process or system.
  • Sequence diagrams are used to model real-time systems, while activity diagrams are used to model business processes or workflows.
  • Sequence diagrams are more detailed and oriented towards implementation, while activity diagrams are more high-level and oriented towards understanding and design.


22. What does Strategy Pattern mean?

Ans: The Strategy Pattern is a design pattern that encapsulates algorithms in separate classes and makes them interchangeable via a common interface. It allows more flexibility and adaptability in the system. It is commonly used in systems where there are multiple ways of achieving a particular goal, and behavior needs to be changed dynamically at runtime.


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

Ans: When I review code written by someone else, I typically follow a process that includes the following:

  • Reviewing the code for readability and style, 
  • Testing it for functionality, 
  • Checking for security vulnerabilities, 
  • Providing specific and constructive feedback to the developer, and 
  • Following up on any changes. 

The goal is to provide feedback that helps the developer improve the code and make it more robust and secure.


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

Ans: As a Low-Level Design (LLD) designer, my experience with technologies has been focused on designing and implementing software systems using a variety of programming languages, frameworks, and libraries.

Some of the technologies I have experience using in my past roles include:


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

Ans: I recently worked on a project redesigning a client's corporate website in the financial services industry. The project aimed to modernize the website and improve the user experience.

In this project, I collaborated with a team of developers, UX designers, and content writers to create a new design for the website. We used technologies such as React for the front-end development and Node.js for the back-end development. We also utilized GraphQL as a data query and manipulation language. My role in the project was to design the website's low-level architecture and data model and provide API specifications for the back end. 


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

Ans: I designed an object-oriented system for a website using React, Node.js, and MongoDB that allowed users to manage their profiles. The system followed an MVC architecture and used OOP principles for flexibility and maintainability. The system had several classes, such as User, Profile, and Connection, organized in a hierarchy for easy reuse and modification. The system also utilized RESTful APIs and JWT for authentication and authorization.


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

Ans: I once encountered a bug in a website built with React, Node.js, and MongoDB that caused an error to be thrown every time a user tried to submit a form. The error message could have been more specific and provided helpful information about the root cause of the problem. I discovered that the database was not correctly indexing the data in one of the fields, which was causing the error.

To fix the issue, I added an index to the database. I also updated the associated APIs to ensure that the data was being queried correctly. I tested the fix thoroughly to ensure it was working as expected.


28. What were your responsibilities in your previous position?

Ans: In my previous position, my primary responsibilities were to 

  • Design the low-level architecture of the system
  • Create the API specifications
  • And do code reviews

I have experience working in scalable and maintainable web applications using React, Node.js, and MongoDB. I designed the system architecture and data model and created the class hierarchy. I also developed the APIs that provided access to the underlying data.

I also reviewed the code and provided feedback to the developers, ensuring that the code was well-designed and adhered to best practices. 
 

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

Ans: As an LLD designer, the low-level Design's most exciting and challenging aspect is creating efficient algorithms to solve complex problems. For example, in a recent project, I had to design a class hierarchy and data model for a social media platform. It was challenging to create a flexible structure to accommodate new features and updates while ensuring that it was easy to understand and maintain. 
 

30. How do you ensure quality and fix errors?

Ans: As an LLD designer, there are several ways that I ensure the quality of the design and fix errors:

  • Peer Reviews: I will take reviews of the design with other designers to identify potential issues or errors.
  • Unit Testing: I will write and execute unit tests to ensure the code functions as expected.
  • Refactoring: I will refactor the code to ensure it adheres to best practices and design principles.
  • Debugging: Using debugging tools and techniques, I will identify and resolve errors in the code.
  • Continuous Integration and Delivery: I will ensure the code is integrated and delivered frequently. It will help to identify and resolve issues early in the development process.
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Conclusion

In this article, we discussed the most-asked Low-Level Design interview questions and also saw their ideal answers. Hope these Low-Level Design interview questions helped you to prepare for the system-designing interviews.

Check out other related articles to learn more: 

Refer to our guided paths on Coding Ninjas Studio to learn more about DSA, Competitive Programming, Javascript, System Design, etc. You can also consider our System Design Course to give your career an edge over others.

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