Infosys Full-Stack Developer Interview Questions

Welcome to the detailed interview guide for Infosys. This page contains specific, extracted interview questions with direct resource links to help you prepare effectively.

1. Coding & Algorithms

Infosys evaluates your problem-solving skills using Data Structures and Algorithms. Below are highly frequent questions asked by Infosys.

Detailed Data Structures & Algorithms Questions

1. Reverse a String / Array (Strings / Two Pointers)
   • Question: Write a function that reverses a string. The input string is given as an array of characters.
   • Resource: LeetCode 344 - Reverse String
2. Valid Palindrome (Strings)
   • Question: Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
   • Resource: LeetCode 125 - Valid Palindrome
3. Find the Duplicate Number (Arrays)
   • Question: Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive, find the duplicate number.
   • Resource: LeetCode 287 - Find the Duplicate Number
4. Detect Loop in Linked List (Linked List)
   • Question: Given head, the head of a linked list, determine if the linked list has a cycle in it.
   • Resource: LeetCode 141 - Linked List Cycle
5. Fibonacci Number (Math / DP)
   • Question: Find the Nth Fibonacci Number. Commonly asked in entry-level screening.
   • Resource: LeetCode 509 - Fibonacci Number

2. Core Full-Stack Technologies

As a Full Stack Developer, Infosys expects you to have a deep understanding of both frontend and backend ecosystems.

Detailed Frontend Questions (React / JavaScript)

1. Virtual DOM & Reconciliation
   • Question: Explain how React's Virtual DOM works and describe the Diffing algorithm.
   • Resource: React Docs - Reconciliation
2. Event Delegation & Bubbling
   • Question: What is event bubbling and capturing in JavaScript? How does Event Delegation improve performance?
   • Resource: JavaScript.info - Bubbling and capturing
3. Promises and Async/Await
   • Question: Write a function to execute an array of Promises sequentially (one after another).
   • Resource: MDN - Using Promises
4. Custom Hooks Implementation
   • Question: Write a custom useDebounce hook that delays invoking a function until after wait milliseconds have elapsed.
   • Resource: useHooks - useDebounce

Detailed Backend Questions (Node.js / Express / DB)

1. Event Loop in Node.js
   • Question: Explain the phases of the Node.js Event Loop. What is the difference between process.nextTick() and setImmediate()?
   • Resource: Node.js Docs - Event Loop
2. Database Indexing & Optimization
   • Question: How do database indexes work under the hood (B-Trees)? When should you NOT use an index?
   • Resource: GeeksForGeeks - Indexing in Databases
3. JWT vs Session Authentication
   • Question: Explain the pros and cons of using JSON Web Tokens (JWT) vs stateful Session cookies for authentication in a distributed system.
   • Resource: Auth0 - JWT vs Sessions
4. API Rate Limiting
   • Question: How would you implement rate limiting for a REST API using Redis?
   • Resource: Redis - Rate Limiting Pattern

3. Architecture & System Design

System design is crucial, especially for mid-to-senior level roles at Infosys.

Detailed System Design / Architecture Questions

1. Monolith vs Microservices
   • Question: Explain the scenarios where a monolithic architecture is preferred over microservices, and vice versa.
   • Resource: Martin Fowler - Microservices
2. Database Schema Design
   • Question: Design a normalized database schema for a Library Management System.
   • Resource: Lucidchart - ER Diagram Tutorial
3. Caching Strategies
   • Question: When would you use Write-Through vs Write-Behind caching?
   • Resource: AWS - Caching Strategies

4. Behavioral & Culture

• STAR Method: Always answer behavioral questions using Situation, Task, Action, Result.
• Why Infosys?: Research Infosys's core values (e.g., Amazon's Leadership Principles, Google's "Googliness", or TCS's client-first approach).
• Resource: How to answer Behavioral Questions

5. Latest 2026 Interview Trends

• Cloud Migration: Questions frequently revolve around migrating legacy monoliths to AWS/Azure, utilizing containerization (Docker/Kubernetes).
• Security & DevSecOps: Expect questions on OWASP Top 10, securing APIs with OAuth2/OIDC, and automated CI/CD pipeline security.
• Modern JavaScript: Extensive focus on TypeScript adoption, strict typing, and migrating large codebases from JavaScript to TypeScript.
• Resource: OWASP Top 10 Web Application Security Risks