How to Prepare for Low Level Design Interview: A Guide

In software development, transforming high-level concepts into fine blueprints is the key to successful project execution.

Low-level design, also called detailed design, is where the grand visions take shape as viable solutions.

It's the phase where your ability to craft efficient, scalable, and maintainable code becomes paramount.

Whether you're a seasoned software engineer or a budding developer, this guide has something for you.

I'll walk you through the ins and outs of Low-Level Design interviews.

⭐We'll talk about how to prepare for low-level design interviews and essential low-level design interview questions.

We'll also cover some practical tips for low-level design interviews.

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What Is the Purpose of Low-Level Design (LLD)?

Low-Level Design (LLD) stands at the core of software development.

It provides a crucial bridge between a High-Level Solution and the practicality of its implementation. 

Often referred to as the "detailed design," LLD serves as the blueprint that brings the system to life!

It defines the logic and functionality of each module.

High-Level Design (HLD) sets the foundation and defines the structure of the system.

But, LLD takes it a step further.

👉 It focuses on the internal structure, algorithms, and data structures of each component.

Thus, providing the necessary guidance for developers to bring the system to life.

Our next question is:

What Can You Expect In an LLD Interview?

In a Low-Level Design interview, the interviewer may ask you to design different types of systems.

Which is to assess your ability to create scalable, flexible, and maintainable software. 

👉 Let's look at a few examples:

1. Class/Entity Design

‍You may be asked to design the classes and entities for specific objects.

Such as a bird, pen, or pizza.

The focus will be on creating appropriate class hierarchies.

Then defining attributes and methods, and considering relationships between objects.

2. Application Design

‍This type of interview involves designing a complete application or system.

Such as a parking lot management system or a booking system like BookMyShow.

Ask clarifying questions, and design the architecture, modules, and interactions between components.

3. Game Design

‍They will assess your ability to create logic and mechanics for games. 

👉 You'll need to define the rules, game states, and design components.

Such as players, moves, and game boards.

During the interview, ask for clarifications if you have any doubts.

They're interested in your approach, problem-solving skills, and understanding of design patterns.

Remember, there's no right or wrong answer!

The goal is to communicate your thoughts clearly.

Break down the problem into smaller components.

And then create a design that fulfils the system's goals. 

With practice, you'll be well-prepared to create well-structured software systems,

Foundations of LLD

By delving into the core principles, you can gain the confidence to solve LLD problems.

An understanding of these topics will be your arsenal in crafting scalable solutions.

1. Object-Oriented Programming

Object-Oriented Programming (OOP) is a programming paradigm.

It focuses on organising software around objects which are instances of classes that encapsulate data and behaviour. 

OOP principles include:

DRY (Don't Repeat Yourself)

Avoid duplicating code.

How?

By promoting code reuse through abstraction, inheritance, and composition.

YAGNI (You Aren't Gonna Need It)

Only implement features and functionality that are required at the moment.

Avoid adding unnecessary complexity based on speculative future needs.

SOLID Design Principles

SOLID is an acronym that represents a set of five design principles.

It helps create maintainable and extensible software:

• Single Responsibility Principle (SRP): A class should have only one reason to change. Meaning it should have a single responsibility.

• Open-Closed Principle (OCP): Software entities (classes, modules, functions) should be open for extension. But closed for modification.

• Liskov Substitution Principle (LSP): Objects of a superclass should be replaceable with objects of their subclasses. That is, without affecting the correctness of the program.

• Interface Segregation Principle (ISP): Should not depend on interfaces they do not use. Interfaces should be focused and specific.

• Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules. Both should depend on abstractions.

👉 You can also read about Star Interview Method.

2. Design Patterns

Design patterns are reusable solutions to common design problems.

They provide a structured approach to solving specific design challenges.

Design patterns into three groups would be:

Creational Patterns

These patterns deal with object creation mechanisms.

👉 Examples: Builder, Factory, Singleton.

Structural Patterns

These patterns focus on the composition of classes and objects.

👉 Examples: Composite, Decorator, Facade.

Behavioural Patterns

These patterns deal with the communication between objects.

👉 Examples: Observer, Strategy, Visitor.

3. UML Diagrams

Unified Modeling Language (UML) is a standardised modelling language.

It is used to visually represent software systems.

There are 14 types of UML diagrams, classified into two main categories:

Structural Diagrams: Represent the static structure of a system.

Behavioural Diagrams: Represent the dynamic behaviour of a system. 

4. Schema Design

It is the process of designing the structure and organisation of a database schema.

It involves identifying entities, defining their relationships, and specifying attributes and constraints.

Proper schema design ensures efficient storage, retrieval, and manipulation of data.

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How to Prepare For a Low-Level Design Interview?

By following these steps, you will be able to analyse and design software systems and boost your low-level design interview preparation.

Systems that exhibit modularity, extensibility, and maintainability.

To solve an LLD problem, you can follow:

1. Clarifying and Gathering Requirements

Solving a problem without knowing what the problem is would be like trying to find a needle in a haystack.

Quite the wild goose chase, wouldn't you agree? 

So, first is understanding the problem at hand! 

Engage with stakeholders, ask insightful questions, and gather detailed requirements.

Clarify any ambiguities.

Ensure a clear understanding of the problem's scope and constraints. 

By grasping the requirements, you lay a strong foundation for the design.

2. Class Diagram and Use Case Diagram

Now, proceed to define the classes, objects, and their relationships. 

👉 Create a class diagram that depicts the structure of the system.

Highlight the essential entities and their associations.

Simultaneously, develop a use case diagram that captures the system's behaviour.

Illustrate how different actors interact with it. 

These visual representations serve as a blueprint for the system's design.

They also aid in conceptualising its architecture.

3. Coding

Once the design is established, it's time to bring the system to life through coding!

Implement the system based on the design decisions made in the previous steps.

👉 Apply object-oriented programming principles.

Such as encapsulation, inheritance, and polymorphism, to create clean and modular code.

Adhere to the SOLID principles.

Ensure that your code is well-structured, maintainable, and extensible.

Leverage appropriate design patterns, such as the Builder, Factory, Singleton, and Observer patterns. 

They will help you address specific design challenges and improve code organisation.

Follow coding best practices. Use meaningful variable and function names.

During the coding phase, also consider the following:

• Break down the system into smaller modules or classes. They will lead to better manageability and reusability.

• Write unit tests to verify the correctness of individual components. It will ensure system functionality.

• Refactor your code when necessary to enhance readability. Drop code smells, and optimise performance.

• Strive for a modular and extensible design. It must allow for future enhancements and changes.

Each step contributes to the process of problem-solving.

It enables you to create high-quality software solutions.

Solutions that meet the requirements of the problem at hand.

Thus, all are important to keep in mind.

Once the design is established, it's time to bring the system to life through coding!

✨Fail-proof your LLD interview prep.

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Tips For Low-Level Design Interview

1. Know your ABCs

‍Brush up on your ABCs of LLD.

👉 That is Object-Oriented Programming, SOLID principles, and design Patterns.

These foundations will be your secret sauce to impress the interviewers.

2. Practice problem-solving

‍Practice creating elegant and scalable architectures.

It should make the interviewers go "Wow!" 

3. Don't be a lone wolf

‍Show your ability to work with a team.

Be open to listen to different perspectives.

After all, great designs are often a collaborative symphony!

4. Keep it simple

Avoid overcomplicating your design.

Simplicity is the key to elegance and maintainability. 

5. Think about extensibility and scalability

‍Consider how your design can accommodate future growth.

Design components that are modular, loosely coupled, and easily extendable.

6. Be a master of disaster (handling)

‍Show your skills in error handling and exception management.

Design a system that handles errors and provides helpful messages. 

7. Showcase your adaptability

This can be shown by discussing how you handle changing requirements. 

8‍. Keep calm and code on

‍Stay calm, confident, and collected throughout the interview.

Remember, the interviewers are looking for your potential and problem-solving abilities.

So, take a deep breath, rock that Low-Level Design interview, and code on with confidence.

👉 Here is Top 5 Tips to Help You Crack Your Next Coding Interview

Low-Level Design Interview Questions to Prepare For

1. Design a Parking Lot

You will be expected to consider the various components.

Such as parking spots, vehicles, entry/exit points, and payment systems. 

Focus on creating an efficient and scalable architecture.

Especially ones that can handle parking spot allocation, vehicle management, and payment processing.

2. Design a Social Media Feed

You'll be asked to design the backend architecture for a social media feed system. 

Consider how you would handle user feeds, user relationships, and post-ranking algorithms. 

Show your understanding of efficient data retrieval, caching mechanisms, and personalised content delivery.

3. Design a File Storage System

This question tests your capacity to design an LLD solution for a file storage system.

👉 You'll need to consider how files are organised, stored, and accessed. 

Think about factors such as file hierarchy, metadata management, and access control.  

Demonstrate your understanding of efficient data structures, indexing mechanisms, and data integrity.

4. Design a Ride-Sharing Service 

You'll be tasked with designing the backend architecture for a ride-sharing service like Uber or Lyft. 

👉 Consider the components such as users, drivers, rides, real-time tracking, and pricing algorithms. 

Showcase your knowledge of location-based services, efficient matching algorithms, and real-time data processing.

5. Design a Hotel Reservation System

Aim to build a system that handles room bookings, availability, pricing, and guest management. 

Consider how you would:

• Structure the database, 
• Handle booking conflicts, and 
• Accommodate various types of rooms and pricing strategies. 

Showcase your understanding of data modelling, concurrency control, and transaction management.

To Sum Up

During a Low-Level Design interview, it's crucial to communicate your thought process.

Justify your design decisions, and showcase your understanding of trade-offs and best practices. 

Remaining calm, confident, and receptive to feedback is key throughout the interview process.

Remember, if you have any further questions feel free to reach out. 

It can be a one-on-one session to address specific doubts.

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