A front-end sudoku generator and solver

Build a complete Sudoku application that can generate puzzles, validate solutions, and solve puzzles using algorithmic approaches. The application should have both a command-line interface and a simple graphical interface.

• Implement a 9x9 grid using a 2D array or matrix
• Use integers 1-9 for filled cells and 0 (or null) for empty cells
• Create a SudokuBoard class with methods for:
  • Getting and setting cell values
  • Checking if a move is valid
  • Displaying the board in a readable format
  • Deep copying the board state

Implement comprehensive validation that checks:

• Row validation: No duplicate numbers 1-9 in any row
• Column validation: No duplicate numbers 1-9 in any column
• 3x3 box validation: No duplicate numbers in any of the nine 3x3 subgrids
• Complete puzzle validation: Verify a fully filled board is a valid solution
• Partial puzzle validation: Check if current state has no conflicts

Implement at least two solving algorithms:

Algorithm 1: Backtracking

• Find empty cell (value 0)
• Try numbers 1-9 in that cell
• For each valid number, recursively solve the rest
• If no solution found, backtrack and try next number
• Include optimization: choose cell with fewest possible values first

Algorithm 2: Constraint Propagation

• Naked singles: If a cell has only one possible value, fill it
• Hidden singles: If a number can only go in one cell in a row/column/box, place it
• Combine with backtracking for harder puzzles

Create a generator that produces valid puzzles with unique solutions:

• Start with a complete, valid Sudoku grid
• Remove numbers systematically while ensuring unique solution
• Support difficulty levels:
  • Easy: 45-50 filled cells, solvable with basic logic
  • Medium: 35-44 filled cells, requires some advanced techniques
  • Hard: 25-34 filled cells, requires complex logical deduction
  • Expert: 17-24 filled cells, may require trial and error

Command Line Interface:

• Display board with clear grid lines and formatting
• Accept input in format "row,col,value" (e.g., "3,7,5")
• Commands: solve, validate, hint, new_game, save, load
• Show solving steps with timing information

Graphical Interface (choose one):

• Web-based (HTML/CSS/JavaScript)
• Desktop (Tkinter, PyQt, Java Swing, etc.)
• Features needed:
  • Clickable 9x9 grid with clear visual separation of 3x3 boxes
  • Number input buttons or keyboard input
  • Solve, validate, hint, and new puzzle buttons
  • Timer and move counter
  • Highlight conflicts in red

File I/O:

• Save/load puzzles in a standard format (plain text or JSON)
• Support importing puzzles from common formats
• Export solved puzzles with solution steps

Hint System:

• Identify next logical move without giving away the answer
• Explain reasoning: "Row 5 can only have a 7 in column 3"
• Progressive hints: start with general area, get more specific

Statistics and Analytics:

• Track solving time and number of moves
• Identify which techniques were used to solve
• Generate difficulty rating for custom puzzles

• Solver should handle most puzzles in under 1 second
• Generator should create new puzzle in under 3 seconds
• Support undo/redo with efficient state management