Khatabook Software Engineer Interview: Rounds, Questions and Preparation

What the job involves

Software engineers at Indian unicorns and high-growth startups like Khatabook build and scale consumer-facing products, often working across the stack to ship features quickly. They collaborate with product, design, and data teams to solve real user problems, with a strong emphasis on performance, reliability, and iterative development. Expect to own modules end-to-end, from coding and testing to deployment and monitoring.

Role and Technical Knowledge

1. 1

   Explain how you would design a database schema for a feature that tracks user transactions in a fintech app.

   Cover tables for users, transactions, and metadata, with indexes on frequent query fields. Discuss normalization, ACID properties, and scalability considerations.

2. 2

   What are the key differences between SQL and NoSQL databases, and when would you choose one over the other for a startup product?

   Highlight structure, scalability, and consistency trade-offs. Relate to use cases like user profiles (SQL) vs. real-time analytics (NoSQL).

3. 3

   How would you optimize an API endpoint that is slow due to high database load?

   Mention caching, query optimization, pagination, and database indexing. Also consider load balancing and asynchronous processing.

4. 4

   Describe how you would implement authentication and authorization for a mobile app backend.

   Discuss JWT or OAuth, secure password storage, role-based access control, and token expiry. Emphasize security best practices.

Practical Scenarios

1. 5

   You are tasked with adding a new feature to an existing codebase with poor documentation. How do you approach it?

   Talk about reading code, writing tests to understand behavior, and collaborating with teammates. Mention incremental changes and documentation as you go.

2. 6

   A production bug is causing intermittent failures for some users. How do you debug and resolve it?

   Outline steps: reproduce, check logs, use monitoring tools, isolate variables, and deploy a fix with rollback plan. Stress communication with the team.

3. 7

   How would you handle a situation where you need to integrate a third-party payment gateway into the app?

   Cover reading API docs, sandbox testing, error handling, and security compliance. Mention idempotency and webhook handling.

4. 8

   You have to deploy a critical update but tests are failing intermittently. What do you do?

   Prioritize identifying flaky tests, run tests locally, and check CI logs. If needed, delay deployment and communicate risks to stakeholders.

Behavioural and HR

1. 9

   Tell me about a time you worked in a team to deliver a project under a tight deadline.

   Use STAR method: describe the situation, your role, actions taken (e.g., prioritization, communication), and the outcome. Highlight teamwork and results.

2. 10

   Why do you want to work at a high-growth startup like Khatabook instead of a larger, more established company?

   Show enthusiasm for fast-paced environments, ownership, and impact. Align with the company's mission and your desire to learn broadly.

3. 11

   Describe a situation where you received constructive criticism. How did you respond?

   Demonstrate openness to feedback, a growth mindset, and concrete steps you took to improve. Avoid being defensive.

4. 12

   Where do you see yourself in the next two years, and how does this role align with your goals?

   Express a desire to grow technically and take on more responsibility. Tie your goals to the company's growth and learning opportunities.

Problem Solving and Coding

1. 13

   How would you find the first non-repeating character in a string? Write the code.

   Use a hash map to count frequencies, then iterate to find the first with count 1. Discuss time and space complexity.

2. 14

   Given an array of integers, find two numbers that add up to a specific target. Explain your approach.

   Use a hash map for O(n) time. Mention brute force vs. optimized solutions and handle edge cases like no solution.

3. 15

   Explain how you would detect a cycle in a linked list.

   Describe Floyd's cycle-finding algorithm (tortoise and hare). Discuss time O(n) and space O(1), and mention alternative using a hash set.

4. 16

   Write a function to reverse a linked list iteratively and recursively.

   Show iterative pointer manipulation and recursive base case. Discuss trade-offs in space and readability.