Sudoku 9x9 Game

The game "Sudoku 9x9" is the most common version of the classic Sudoku, which is a true original. The main features is the playing field size of 9 by 9 squares, which in total is 81 squares. The playing field has a square shape and is conditionally divided into 9 more small squares, each containing 9 cells. You need to fill in all the cells on the playing field observing the rules described below. The game has 3 modes of difficulty, namely: beginner, normal, advanced. Each difficulty differs from the others only in the number of original numbers, which are present on the playing field.