Sudoku Solver

Sudoku puzzle solver built in C++17 with SFML 2.5+.

• Backtracking solver with MRV (Minimum Remaining Values) heuristic
• Live conflict detection — violating cells highlight in red as you type
• Same-number highlighting — selecting a cell highlights all matching digits
• Solve animation — filled cells pulse blue when the puzzle is solved
• Full keyboard support — arrows navigate, digits input, Backspace clears
• Three buttons: Solve, Clear (keep puzzle), Reset (blank slate)

sudoku/
├── CMakeLists.txt
├── README.md
├── assets/
│   └── fonts/
│       ├── Inter-Regular.otf
│       ├── Inter-Medium.otf
│       ├── Inter-SemiBold.otf
│       └── Inter-Bold.otf
└── src/
    ├── main.cpp          — Entry point
    ├── SudokuGrid.hpp/cpp — 9×9 board model + constraint checks
    ├── Solver.hpp/cpp     — MRV-enhanced backtracking solver
    └── GUIApp.hpp/cpp     — SFML window, events, rendering

Owns the 9×9 int board_[9][9] array (0 = empty) and a parallel bool given_[9][9] mask distinguishing pre-filled cells from solver-filled ones. Exposes isValidPlacement(row, col, value) for constraint checking and a public conflict[9][9] display-metadata array.

Stateless. solve(grid) runs recursive backtracking; findBestEmpty() applies MRV to pick the most-constrained empty cell first, cutting the search tree significantly. markConflicts(grid) sweeps every filled cell to flag violations for the GUI.

Manages the SFML RenderWindow, event loop, and all drawing. Separated into:

• handleEvent / handleMouseClick / handleKeyPress — input
• update(dt) — animation clock
• drawBackground / drawGridShadow / drawCells / drawGridLines / drawNumbers / drawButtons / drawStatusText — rendering pipeline

# 1. Install SFML
#    Ubuntu/Debian:
sudo apt install libsfml-dev

#    macOS (Homebrew):
brew install sfml

# 2. Install Inter font (optional — falls back to DejaVu Sans)
#    Ubuntu/Debian:
sudo apt install fonts-inter
#    Then copy to assets/fonts/ (already done if cloned from repo):
cp /usr/share/fonts/opentype/inter/Inter-*.otf assets/fonts/

# 3. Configure & build
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make -j$(nproc)

# 4. Run (from the build directory)
./sudoku

# Assumes SFML extracted to C:\SFML
cmake .. -DSFML_DIR="C:/SFML/lib/cmake/SFML" -DCMAKE_BUILD_TYPE=Release
cmake --build . --config Release

Copy the four SFML DLLs (sfml-graphics-2.dll, sfml-window-2.dll, sfml-system-2.dll, openal32.dll) next to sudoku.exe.

1. Click any cell and type a digit (1–9) to enter your puzzle.
2. Use arrow keys to navigate between cells; Backspace to erase.
3. Press Solve (or Enter/S) to solve the puzzle.
   • Pre-filled numbers remain dark/bold.
   • Solver-filled numbers appear in blue.
4. Press Clear (C) to wipe the solution and restore your input.
5. Press Reset (R) to blank the entire board.

Any digit that violates a row, column, or 3×3 box constraint turns red in real time as you type — no need to wait until you press Solve.

The solver uses backtracking with MRV:

1. Find the empty cell with the fewest legal values (most constrained).
2. Try each digit that doesn't violate any constraint.
3. Recurse; if no digit works, backtrack and try the next candidate in the parent call.

MRV typically reduces solve time from milliseconds to microseconds on human-grade puzzles, and handles "hardest" puzzles (e.g. the Arto Inkala puzzle) in < 1 ms on modern hardware.