CodeBreaker Duel

A real-time, two-player number guessing game built with Node.js, Express, and Socket.IO.

Game Rules

1. Each player secretly chooses a 4-digit number with unique digits (e.g., 1234)
2. Players take turns guessing each other's numbers
3. After each guess, you'll see:
   • Correct Digits: How many digits exist in the secret number
   • Correct Positions: How many digits are in the correct position
4. First player to guess correctly wins

Quick Start

Installation

npm install

Run the Application

npm start

The game will be available at http://localhost:3000

How to Play

1. Create a Session: Click "Create New Session" to start a game
2. Share Code: Share the 6-character session code with your friend
3. Join Session: Your friend enters the code to join
4. Choose Numbers: Both players select their secret 4-digit numbers
5. Play: Take turns guessing until someone wins

Project Structure

ai-coding-challenge/
├── server.js           # Express + Socket.IO server
├── package.json        # Dependencies and scripts
├── public/
│   ├── index.html     # Game UI
│   ├── styles.css     # Styling
│   └── game.js        # Client-side game logic
└── README.md

Architecture

Backend (Node.js + Express + Socket.IO)

• Multi-session support: Handles multiple concurrent games
• Real-time communication: WebSocket-based instant updates
• Game logic: Validates numbers, checks guesses, manages turns
• In-memory storage: Fast session management

Frontend (Vanilla JavaScript)

• Single-page application: Smooth screen transitions
• Real-time updates: Instant feedback on all actions
• Responsive design: Works on desktop and mobile
• User-friendly: Clear visual feedback and intuitive flow

Features

• Session Management: Create and join games with unique codes
• Real-time Sync: WebSocket-based instant updates
• Multiple Sessions: Support for unlimited concurrent games
• Turn Management: Automatic turn alternation
• Input Validation: Ensures valid 4-digit unique numbers
• Game History: View all guesses and results
• Responsive UI: Works on all devices
• Error Handling: Graceful disconnection handling
• Scalable Architecture: Ready for production deployment

Technology Stack

• Backend: Node.js, Express.js
• Real-time: Socket.IO
• Frontend: HTML5, CSS3, Vanilla JavaScript
• Deployment: Render, Railway, or Heroku

Development

Local Development

npm install
npm run dev

Testing Multiplayer Locally

1. Open http://localhost:3000 in one browser window
2. Create a session and copy the code
3. Open http://localhost:3000 in another browser window (or incognito)
4. Join with the code and play

Game Logic Details

Number Validation

• Must be exactly 4 digits
• All digits must be unique
• Only numeric characters allowed

Guess Checking

• Correct Digits: Counts how many digits from the guess exist anywhere in the secret number
• Correct Positions: Counts how many digits are in the exact right position
• Example: Secret = 1234, Guess = 1543
  • Correct Digits: 4 (all digits exist)
  • Correct Positions: 2 (1 and 4 are in correct positions)

Scalability

The current architecture supports:

• Multiple concurrent game sessions
• Real-time WebSocket connections
• In-memory session storage

For production scale:

• Database: Add Redis for session persistence
• Load Balancing: Use Socket.IO Redis adapter for multiple instances
• CDN: Serve static assets via CDN
• Monitoring: Add logging and analytics

License

MIT License - Feel free to use for your projects.

Contributing

Contributions welcome! Feel free to open issues or submit pull requests.