Cars24 Full Stack Developer Interview: Rounds, Questions and Preparation

What the job involves

Full Stack Developers at Indian unicorns and high-growth startups build and maintain both the customer-facing frontend and the backend services that power fast, scalable products. You will work across the stack, from React or Vue interfaces to Node.js or Java APIs and databases, often shipping features weekly in a fast-paced, metrics-driven environment. Expect close collaboration with product, design, and DevOps teams to optimise for performance, reliability, and user experience at scale.

Role and Technical Knowledge

1. 1

   How would you design a REST API for a used-car listing platform where users can filter by make, model, year, and price range?

   Cover endpoint structure, query parameters, pagination, and indexing strategies for fast filtering on large datasets.

2. 2

   Explain the difference between server-side rendering and client-side rendering in the context of a high-traffic e-commerce site.

   Discuss SEO, initial load time, and server load, and mention when to use Next.js or similar frameworks.

3. 3

   What are the trade-offs between SQL and NoSQL databases for storing vehicle inventory and user sessions?

   Compare consistency, scalability, and query flexibility, and suggest a polyglot persistence approach if needed.

4. 4

   How do you ensure a React component re-renders only when necessary in a complex dashboard?

   Mention React.memo, useCallback, useMemo, and understanding of virtual DOM diffing.

Practical Scenarios

1. 5

   A critical API endpoint is timing out during peak traffic. How would you debug and fix it?

   Walk through checking logs, database query plans, caching layers, and adding rate limiting or horizontal scaling.

2. 6

   You need to add a real-time chat feature for buyers and sellers. What stack and architecture would you choose?

   Discuss WebSockets, Socket.io, message queues, and scaling with Redis pub/sub.

3. 7

   How would you implement a CI/CD pipeline for a full-stack app with separate frontend and backend repos?

   Cover automated testing, build steps, environment variables, and deployment to cloud platforms like AWS or Vercel.

4. 8

   A bug is reported only on older Android devices for a React app. How do you approach fixing it?

   Mention browser/device testing, polyfills, transpilation with Babel, and using tools like BrowserStack.

Behavioural and HR

1. 9

   Tell me about a time you had to learn a new technology quickly for a project. How did you manage?

   Use STAR method, highlight self-learning, and connect it to delivering results under deadline.

2. 10

   Describe a situation where you disagreed with a teammate on a technical approach. How did you resolve it?

   Show empathy, data-driven discussion, and willingness to compromise for the team's goal.

3. 11

   Why do you want to work at a fast-growing startup like Cars24 rather than a large MNC?

   Express excitement for ownership, rapid iteration, and direct impact on users, and research the company's mission.

4. 12

   How do you prioritise tasks when you have multiple deadlines and limited time?

   Mention frameworks like Eisenhower matrix, communicating with stakeholders, and focusing on high-impact work.

Problem Solving and Code Quality

1. 13

   Write a function to find the first non-repeating character in a string. Explain your approach and time complexity.

   Use a hash map for O(n) time, and discuss edge cases like empty string or all repeating characters.

2. 14

   How would you optimise a slow SQL query that joins multiple tables for a reporting dashboard?

   Talk about indexing, avoiding SELECT *, using EXPLAIN, and denormalisation for read-heavy workloads.

3. 15

   Given an array of integers, find two numbers that sum to a target. How would you handle large inputs?

   Use a hash set for O(n) time, and discuss memory trade-offs and streaming if data does not fit in memory.

4. 16

   What steps do you take to ensure your code is maintainable and testable?

   Mention modular design, unit tests, code reviews, and following style guides and linting.