Qlik India Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers in global tech companies build and maintain server-side logic, APIs, and databases that power web and mobile applications. At product companies like Qlik India, this often involves working with large datasets, ensuring low-latency responses, and integrating with analytics or data pipelines. Day to day, you write code, review peers' code, debug production issues, and collaborate with frontend and data teams.

Role and technical knowledge

1. 1

   What happens when you type a URL into a browser and hit enter, from a backend perspective?

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

2. 2

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

   Highlight schema flexibility, scaling, and consistency trade-offs. For BI dashboards, SQL often suits structured, relational data, while NoSQL may handle unstructured or high-velocity data.

3. 3

   How does indexing work in a database, and why is it important for backend performance?

   Explain that indexes speed up read queries by creating a data structure (like B-tree) but slow down writes and use extra storage. Give an example of a query that benefits.

4. 4

   What is a REST API, and what are the key principles behind it?

   Mention statelessness, client-server separation, uniform interface, and use of HTTP methods. Contrast with SOAP or GraphQL briefly if asked.

Practical scenarios

1. 5

   You are building an API that returns a large dataset for a dashboard. How would you ensure it responds quickly?

   Discuss pagination, filtering, caching, database indexing, and asynchronous processing. Mention compression and CDN for static assets.

2. 6

   A production server is running out of memory. How would you debug and fix it?

   Outline checking logs, monitoring tools, memory profiling, identifying leaks or inefficient code, and scaling vertically or horizontally. Mention restarting as a temporary fix.

3. 7

   How would you design a simple URL shortener service?

   Cover generating unique short codes, storing mappings in a database, handling redirects, and considering scalability and collision avoidance.

4. 8

   You need to add a new feature that requires changing the database schema. How do you approach it with minimal downtime?

   Discuss backward-compatible migrations, blue-green deployment, and testing on a staging environment. Mention using tools like Flyway or Liquibase.

Behavioural and HR

1. 9

   Tell me about a time you worked in a team to solve a technical problem. What was your role?

   Use STAR method: describe the situation, task, action, and result. Highlight collaboration, communication, and your specific contribution.

2. 10

   Why do you want to work as a backend engineer at a global tech company like Qlik India?

   Show interest in large-scale data challenges, product impact, and learning opportunities. Connect your skills to the company's domain without claiming insider knowledge.

3. 11

   Describe a situation where you had to learn a new technology quickly for a project.

   Emphasize self-learning, resourcefulness, and applying the new skill effectively. Mention specific resources or methods you used.

4. 12

   Where do you see yourself in five years?

   Align your growth with technical depth and leadership. Show commitment to backend engineering and continuous learning.

Coding and problem-solving

1. 13

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

   Cover iterative and recursive solutions, time and space complexity, and edge cases like empty list or single node.

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 a hash map for O(n) time. Discuss trade-offs and handle duplicates.

3. 15

   How would you detect a cycle in a linked list?

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

4. 16

   Implement a stack that supports push, pop, and retrieving the minimum element in O(1) time.

   Use an auxiliary stack to track minimums. Explain how to update it on push and pop. Discuss space complexity.