The Most Common Low Level Design Interview Questions and How to Approach Them

Low level design (LLD) interview questions are an essential part of the hiring process for many software engineering roles. LLD focuses on the implementation and technical details of a system, as opposed to high level design which looks at the broader architecture and workflows. Mastering common LLD interview questions is key to showcasing your skills in translating requirements into concrete design and code.

In this comprehensive guide, we will look at some of the most frequently asked LLD interview questions, along with proven strategies and examples to help you ace these interviews

Why Low Level Design Questions are Important in Interviews

LLD questions test your ability to drill down into the minute details of system implementation. Interviewers want to assess your technical knowledge and evaluate your approach to breaking down complex problems. Key areas evaluated include:

• Understanding of core object oriented concepts and design principles
• Knowledge of data structures and algorithms
• System modeling using UML diagrams
• Modularizing the system and identifying key classes/objects
• Defining clean interfaces and APIs
• Handling tradeoffs around performance, scalability, maintainability etc.

Strong low level design skills directly correlate with your ability to write clean, well-structured code LLD interview performance is a good indicator of your technical abilities as an engineer beyond just coding

The Most Common LLD Interview Questions

Here are some of the most popular LLD questions asked in interviews at top technology companies:

Design a parking lot

This open ended LLD question tests your object oriented analysis and design skills Key considerations include

• Requirements gathering (capacity, parking spots, vehicle types)
• Identifying core objects (parking lot, level, spot, vehicle etc)
• Parking strategies (sequential, nearest first etc)
• Search based on vehicle number/type
• Testing edge cases

UML class and activity diagrams can help visualize the classes, relationships, and workflow. Focus on clearly explaining your thought process.

Design a movie ticket booking system

This question evaluates your ability to design real world systems involving multiple entities with varied interactions. Core aspects are:

• Entities – theaters, movies, shows, tickets, users
• Use cases – add theaters/movies, book tickets, cancel tickets etc.
• Managing availability of seats
• Notification of new movie/show additions to theaters
• Searching movies by theater or vice versa

Using UML diagrams, interfaces, and database schema designs will demonstrate a structured approach. Discuss tradeoffs and optimizations.

Design an API rate limiting system

Rate limiting prevents API abuse by restricting number of requests. This question tests your understanding of:

• Requirements gathering (requests per timeframe, handling bursts)
• Data structures like token buckets and request queues
• Algorithms like leaky bucket and fixed window counter
• Optimizing for performance and accuracy

Suggest multiple approaches and analyze the pros and cons of each.

Design a linked list

While this coding interview style question seems simple, it evaluates strong object oriented design abilities:

• Defining Node and LinkedList classes
• Methods like add, remove, traverse
• Optimizing for common operations
• Handling edge cases like empty list or null nodes

Discussion around memory management, efficiency, and testing approach is expected.

Design a cache system

Caching improves performance by storing frequently accessed data for fast retrieval. Key aspects are:

• Cache capacity constraints
• Eviction policies like LRU, LFU, FIFO
• Read/write optimizations
• Cache updates and consistency
• Distributed caching architecture and coordination

This question tests both your system design and algorithm analysis skills.

Best Practices for Answering LLD Interview Questions

Approaching LLD interview questions systematically will greatly improve your performance. Keep these tips in mind:

• Ask clarifying questions – Get clear requirements around use cases, scale, data volumes etc. before designing the system.

• Think out loud – Communicate your thought process clearly. The interviewer wants insights into your analytical skills.

• Start high level – Outline major components and relationships first before diving into implementation details.

• Use examples – Relate the design to real world examples or analogous systems the interviewer is familiar with.

• Modularize – Break the system into logical modules or services and define clear interfaces between them.

• Diagrams help – UML diagrams visually convey your design and make relationships clear. But focus more on explaining your ideas.

• Trades offs matter – Discuss different approaches and analyze the tradeoffs around metrics like performance, scalability, availability etc. There are usually no “perfect” solutions.

• Ask for feedback – Confirm if your design meets the requirements and if the interviewer needs any clarification. Modify your design based on inputs.

Preparation and practice are vital for feeling confident during LLD interviews. Use common interview questions to sharpen your skills and walk through designs end-to-end before the big day. Keep learning new techniques and frameworks to expand your low level design toolkit over time.

Great low level design skills demonstrate your readiness for complex development work and leadership roles. Succeeding in these interviews can significantly impact your software engineering career. Use the strategies above to showcase your technical strengths during your upcoming LLD interview!