How to Play:
Fill the grid with numbers from 1 to 9 so that each column, row, and 3x3 subgrid should not contain the same number more than once.
Keyboard Controls:
Arrow keys / WASD - Navigate the grid
1-9 - Enter numbers
Delete/Backspace - Clear cell
Enter - Check solution (when no cell is focused)
Shift+Enter - Check solution (anytime)
Shift+1-5 - Change difficulty level
r - New game
i - Show/hide this info