Sudoku description

Sudoku is played with 9x9 grid, divided into 3x3 subgrids called "regions".

The object is to fill empty cells with numbers between 1 and 9, so that number should appear only once on each row, column and region.

Easy, Medium and Difficult games have a unique solution. Nightmare games have multiple solutions.

Many settings:
- for Tablets and Phones
- autosave
- statistics
- unlimited Undos
- mode Easy, Normal, Difficult, Nightmare