A feature-rich, interactive Sudoku game built with vanilla HTML, CSS, and JavaScript. Play classic Sudoku puzzles with multiple difficulty levels, hints, and a built-in timer.

• Easy: 35 cells removed, includes error checking and real-time validation
• Medium: 45 cells removed (default)
• Hard: 55 cells removed

• Automatic timer that starts when you begin playing
• Displays elapsed time in MM:SS format
• Resets with each new game

• Toggle hints on/off to show possible valid numbers for empty cells
• Contextual feedback in Easy mode (correct/incorrect number validation)
• Hints automatically clear when you enter a number

• Keyboard Navigation: Use arrow keys to move between cells
• Number Input: Press 1-9 to enter numbers
• Clear Cells: Press Backspace, Delete, or 0 to clear
• Mouse Support: Click any cell to select it

• Check Solution: Validate your current progress
• Show Solution: Instantly reveal the complete solution
• New Game: Generate fresh puzzles anytime

1. Open the Game: Open sudoku.html in your web browser
2. Select Difficulty: Choose Easy, Medium, or Hard from the dropdown
3. Fill the Grid: Click cells and enter numbers 1-9
4. Use Hints: Click the "Hint" button to see possible numbers for empty cells
5. Navigation: Use arrow keys or mouse to move between cells
6. Check Progress: Use "Check Solution" to validate your current state
7. Win: Complete the puzzle with all correct numbers!

Fill the 9×9 grid so that every row, column, and 3×3 box contains the digits 1-9 exactly once.

• Puzzle Generation: Uses recursive backtracking to create valid, solvable Sudoku puzzles
• Real-time Validation: Checks row, column, and 3×3 box constraints
• Smart Hint System: Calculates all possible valid numbers for any cell
• Adaptive Difficulty: Removes different numbers of cells based on selected difficulty

• Object-Oriented Design: Clean SudokuGame class with separated concerns
• Event-Driven: Responsive keyboard and mouse interactions
• State Management: Maintains separate board, solution, and hint states
• Efficient Algorithms: Fisher-Yates shuffle for randomization, Set data structures for optimization

Works in all modern browsers with JavaScript enabled. No external dependencies required.

• sudoku.html - Main game interface and structure
• sudoku.css - Styling and responsive layout
• sudoku.js - Core game logic and algorithms

1. Clone or download the project files
2. Open sudoku.html in any modern web browser
3. Start playing immediately - no installation required!

The game is easily customizable:

• Modify difficulty levels in the newGame() method
• Adjust styling in sudoku.css
• Add new features by extending the SudokuGame class

Enjoy playing Sudoku! 🧩