Linear India Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at fast-growing global tech companies build and maintain the server-side systems that power web and mobile products. They design APIs, manage databases, optimise performance, and ensure reliability at scale. Day to day, they write code, review peers' work, debug production issues, and collaborate with frontend and product teams.

Role and Technical Knowledge

1. 1

   What happens when you type a URL into a browser and press Enter, from a backend perspective?

   Cover DNS resolution, TCP handshake, HTTP request, server processing, database queries, and response. Mention caching and load balancers if relevant.

2. 2

   How would you design a REST API for a simple task management app?

   Define resources (users, tasks), use proper HTTP methods and status codes, include pagination, authentication, and versioning. Discuss trade-offs.

3. 3

   Explain the difference between SQL and NoSQL databases. When would you choose one over the other?

   Compare schema flexibility, scalability, consistency models, and use cases. Give examples like PostgreSQL vs MongoDB for a social feed.

4. 4

   What are indexes in a database and how do they improve performance?

   Explain how indexes speed up reads but slow down writes, and mention B-trees. Discuss when to avoid over-indexing.

Practical Scenarios

1. 5

   Your API response time suddenly spikes from 100ms to 2 seconds. How do you debug and fix it?

   Check logs, metrics, and database slow queries. Look for recent deployments, N+1 queries, or external service issues. Suggest profiling and caching.

2. 6

   You need to add a new feature that requires a database schema change. How do you handle it without downtime?

   Discuss backward-compatible migrations, adding columns with defaults, dual-writes, and feature flags. Emphasise testing and rollback plans.

3. 7

   How would you implement rate limiting for an API to prevent abuse?

   Mention token bucket or sliding window algorithms, using Redis for counters, and returning 429 status. Discuss per-user vs per-IP limits.

4. 8

   A teammate's code works locally but fails in production. How do you approach resolving it?

   Compare environments, check configs, dependencies, and environment variables. Use logs and reproduce with production-like data.

Behavioural and HR

1. 9

   Tell me about a time you had to learn a new technology quickly for a project.

   Use STAR method: describe the situation, the tech, how you learned, and the outcome. Highlight resourcefulness and impact.

2. 10

   Describe a situation where you disagreed with a teammate. How did you handle it?

   Show empathy, focus on data and user impact, and how you reached a consensus. Avoid blaming others.

3. 11

   Why do you want to work at a fast-growing company like Linear India?

   Research the company's product, culture, and engineering blog. Connect your skills and desire to learn with their mission.

4. 12

   Where do you see yourself in three years?

   Align with the company's growth: deepening backend expertise, taking ownership, and mentoring. Show commitment to learning.

Coding and Algorithms

1. 13

   Given a list of integers, find two numbers that sum to a target. How would you optimise it?

   Start with brute force O(n^2) then use hash map for O(n). Discuss edge cases and space-time trade-off.

2. 14

   How would you detect a cycle in a linked list?

   Explain Floyd's tortoise and hare algorithm. Mention alternative using hash set and when each is preferable.

3. 15

   Write a function to reverse a string in place. What is the time and space complexity?

   Use two pointers swapping from ends. O(n) time, O(1) space. Clarify if Unicode or mutable strings are involved.

4. 16

   Given a binary tree, how do you find its maximum depth?

   Use recursion (DFS) or BFS with queue. Discuss iterative vs recursive and handling large trees.