iZooto Software Engineer Interview: Rounds, Questions and Preparation

What the job involves

Software Engineers at Indian SaaS and B2B product companies build and maintain web applications, APIs, and data pipelines that power subscription-based products used by businesses. Day to day, they write code, fix bugs, review pull requests, and work with product managers to ship features that improve customer retention and revenue. Freshers typically start on smaller modules or internal tools, learning the codebase and agile processes.

Role and Technical Knowledge

1. 1

   What is the difference between a REST API and a GraphQL API, and when would you choose one for a B2B SaaS product?

   Explain that REST uses fixed endpoints while GraphQL lets clients request specific data. For B2B SaaS, GraphQL can reduce over-fetching for complex dashboards, but REST is simpler for standard CRUD and caching.

2. 2

   How would you design a database schema for a multi-tenant SaaS application where each customer has isolated data?

   Mention tenant_id columns, row-level security, or separate schemas. Discuss trade-offs between shared and isolated databases for cost and compliance.

3. 3

   Explain the concept of idempotency in APIs and why it matters for payment or subscription endpoints.

   Define idempotency as repeating the same request having the same effect. For payments, use idempotency keys to avoid double charges when clients retry.

4. 4

   What are webhooks, and how would you implement a reliable webhook delivery system for a SaaS product?

   Describe webhooks as user-defined HTTP callbacks. Cover retries with exponential backoff, logging, and a queue to handle failures without blocking the main application.

Practical Scenarios

1. 5

   A customer reports that their dashboard is loading slowly. How would you debug and fix this issue?

   Start by checking server response times, database query performance, and frontend rendering. Suggest profiling, adding indexes, caching, or paginating large data sets.

2. 6

   You need to add a new feature that sends email notifications to users when their subscription is about to expire. Walk me through your approach.

   Outline a scheduled job or cron that checks expiry dates, queues emails, and uses a template service. Mention testing with a staging environment and handling time zones.

3. 7

   How would you handle a situation where a bug in production is causing some users to see incorrect billing amounts?

   Prioritize stopping the issue (feature flag or rollback), then investigate logs and data. Communicate with affected users and add tests to prevent recurrence.

4. 8

   You are asked to improve the performance of a slow SQL query that joins three tables. What steps would you take?

   Use EXPLAIN to analyze the query plan, check indexes on join columns, and consider denormalization or caching. Test changes on a copy of production data.

Behavioural and HR

1. 9

   Why do you want to work in a SaaS or B2B product company rather than a service-based IT firm?

   Show interest in building products that solve business problems, continuous learning, and working closely with product teams. Mention the faster feedback loop and ownership.

2. 10

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

   Use a specific example from college or internship. Highlight self-learning through documentation, online courses, and building a small prototype to test understanding.

3. 11

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

   Focus on data-driven discussion, listening to their perspective, and finding a compromise or running a small experiment to decide. Avoid blaming others.

4. 12

   Where do you see yourself in three years, and how does this role fit into that plan?

   Align your growth with becoming a strong product engineer, taking ownership of modules, and contributing to architecture. Show commitment to learning and the company's domain.

Coding and Problem Solving

1. 13

   Write a function to find the first non-repeating character in a string. What is the time and space complexity?

   Use a hash map to count frequencies, then iterate to find the first character with count 1. Time O(n), space O(n).

2. 14

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

   Start with brute force O(n^2), then improve to O(n) using a hash set to store complements. Explain the trade-off.

3. 15

   How would you implement a function to check if a binary tree is a valid binary search tree?

   Use recursion with min and max bounds, or do an in-order traversal and check if the result is sorted. Discuss edge cases like duplicate values.

4. 16

   Write a SQL query to find the top 3 customers by total order value in the last month.

   Use GROUP BY customer_id, SUM(order_value), filter by date, ORDER BY sum DESC, LIMIT 3. Mention handling nulls and date functions.