Salesken Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

A backend engineer at an Indian SaaS or B2B product company builds and maintains the server-side systems that power web and mobile applications. Day to day, you write APIs, design database schemas, integrate third-party services, and ensure the product handles real-time data and high traffic reliably. You work closely with frontend, product, and DevOps teams to ship features that solve business problems for enterprise customers.

Role and technical knowledge

1. 1

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

   Cover structured vs unstructured data, scalability, and use cases like transactional records (SQL) vs real-time analytics or flexible schemas (NoSQL).

2. 2

   What happens when you type a URL in the browser and press enter? Focus on the backend parts.

   Mention DNS resolution, HTTP request, load balancer, web server, application server, database query, and response. Highlight caching and CDN if relevant.

3. 3

   How would you design a REST API for a simple task management feature in a B2B product?

   Talk about resources (tasks, users), HTTP methods (GET, POST, PUT, DELETE), status codes, authentication (JWT), and versioning.

4. 4

   What is the difference between authentication and authorization? Give an example in a SaaS context.

   Authentication verifies identity (login), authorization checks permissions (e.g., admin vs regular user can access certain APIs).

Practical scenarios

1. 5

   You notice an API endpoint is slow. How would you debug and improve its performance?

   Suggest checking logs, profiling database queries, adding indexes, caching, and optimizing code. Mention tools like New Relic or slow query logs.

2. 6

   A customer reports that their data is not updating in real time. How would you investigate?

   Walk through checking the data pipeline: client request, API logs, database writes, and any message queues. Suggest testing with a sample request.

3. 7

   How would you handle a situation where your code passes tests locally but fails in production?

   Compare environments: dependencies, environment variables, database versions, and network config. Suggest using staging and logging.

4. 8

   You need to integrate a third-party payment gateway. What steps would you take?

   Mention reading API docs, handling authentication, testing in sandbox, error handling, and securing sensitive data.

Behavioural and HR

1. 9

   Tell me about a time you worked in a team to build something. What was your role?

   Use STAR method: describe the project, your specific contribution, and the outcome. Highlight collaboration and communication.

2. 10

   Why do you want to work at a SaaS company like Salesken?

   Show interest in B2B products, solving real business problems, and learning scalable systems. Mention Salesken's domain if you know it.

3. 11

   Describe a challenging technical problem you faced and how you solved it.

   Pick a project or assignment. Explain the problem, your approach, the solution, and what you learned.

4. 12

   Where do you see yourself in three years?

   Align with growth in backend engineering, taking ownership, and contributing to product success. Avoid saying you want to switch domains.

Coding and problem solving

1. 13

   Write a function to reverse a linked list. Explain your approach.

   Use iterative or recursive method. Discuss time and space complexity (O(n) time, O(1) space for iterative).

2. 14

   Given an array of integers, find two numbers that sum to a target. How would you optimize it?

   Start with brute force O(n^2), then use hash map for O(n) time. Mention edge cases like duplicates.

3. 15

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

   Use a hash map to count frequencies, then iterate to find first with count 1. Discuss O(n) time and space.

4. 16

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

   Use Floyd's cycle-finding algorithm (tortoise and hare) with two pointers. Explain why it works and complexity.