Fullstack Developer

How would you design and implement an email broadcast system while minimizing cost, infrastructure, and operational overhead? Explain your approach theoretically.

How do chat applications implement real-time typing indicators efficiently while minimizing network overhead?

How would you design and scale the data storage layer for a globally distributed chat application that serves millions of concurrent users?

What data structures and algorithms would you use to maintain and serve a real-time leaderboard (top N) at scale, and how would you ensure both low latency and accuracy?

Use any Vibe coding tool (such as GitHub Copilot, Claude Code, v0.dev, Lovable, Bolt, Cursor, etc.) to create a research paper tracker for academics and researchers (web application).

Requirements:

Option to add research papers with the following fields:

• Paper Title: Text field
• First Author Name: Text field
• Research Domain: One of: Computer Science, Biology, Physics, Chemistry, Mathematics, Social Sciences
• Reading Stage: One of: Abstract Read, Introduction Done, Methodology Done, Results Analyzed, Fully Read, Notes Completed
• Citation Count: Number
• Impact Score: One of: High Impact, Medium Impact, Low Impact, Unknown
• Date Added: Date field

Option to view the paper library with filtering options (multiple filters can be chosen):

• Reading Stage: Multiple options can be selected
• Research Domain: Multiple options can be selected
• Impact Score: Multiple options can be selected
• Date Added: This Week, This Month, Last 3 Months, All Time

Option to view reading analytics, including:

• Funnel chart showing paper count at each Reading Stage
• Scatter plot with Citation Count on the x-axis and papers grouped by Impact Score
• Stacked bar chart showing papers by domain and reading stage
• Summary: Papers by reading stage, average citations per domain, completion rate (Fully Read / Total)

Guidelines:

• Create a web application meeting the above requirements.
• Sign-in/Signup is optional.
• You can deploy on Vercel, Netlify, Supabase, or any similar platform of your choice.
• You can use React for the frontend and Node.js/Express for the backend.
• Must use a proper database (PostgreSQL, MongoDB, MySQL, or Supabase) to store data persistently.
• You can use any design system of your choice, such as Ant Design, ShadCN, or Material-UI for the UI.
• The app should be built as per the exact requirements, without deviation.
• You can create a UI that is good enough using any design system.

Deadline:
Complete the assignment within 2 days.

What do abstraction, encapsulation, and polymorphism mean in object-oriented programming? (Learn)

Explain time complexity and space complexity, and their roles in algorithm analysis.

You are building an API rate limiter for a backend service.
Each user is allowed to make at most K requests within a rolling window of T seconds.

Function:

boolean allowRequest(userId, timestamp)

Rules:

• userId is a string.
• timestamp is an integer representing seconds.
• Return true if the request is allowed.
• Return false if the user has already made K requests in the last T seconds.

Example:

K = 3, T = 10

allowRequest("user1", 1)   → true
allowRequest("user1", 2)   → true
allowRequest("user1", 3)   → true
allowRequest("user1", 4)   → false
allowRequest("user1", 10)  → false

Develop a React application with 10 cards, each containing a title, content, and a like button. Implement functionality to increment the like count when the button is clicked, apply hover and focus effects to the cards, prevent event propagation from the button, and optimize rendering so that only the updated card re-renders.

What tech stack do you specialize in? Would you consider yourself more frontend- or backend-oriented, and why? Can you also share details about any creative projects you have built?

Why are you leaving your current organization? Please explain your past internship and job experiences, including why you transitioned from those roles. What motivates you, and what does your ideal company look like?

We had a discussion:

Given an array containing 10,000 mobile numbers and a single promotional message, there is a WhatsApp API that accepts only one mobile number and one message per request. Write pseudocode to send the promotional message to all the mobile numbers using this API.

Now, if the API has a limitation of processing only 10 requests per second, how would you modify the code?

How long would it take for the API to process all requests?

What would change if we had one million numbers instead?

Explain how WhatsApp works at a high level. Design a database schema to illustrate user-to-user chats, user interactions with chats, and how WhatsApp Business accounts manage and initiate conversations.