Sudoku Pro

Sudoku is a old logic game with numbers. Goal of the game is to fill 9x9 square box.
There are 9 3x3 square boxes in a large box, and each 3x3 square box can
hold numbers from 1 to 9 (1,2,3,4,5,6,7,8,9) without repeating one
number twice. That means that all 9 boxes must contain all numbers
from 1 to 9, and the whole 9x9 box must contain each number from 1 to
9 nine times (9x1, 9x2, 9x3, 9x4, 9x5, 9x6, 9x7 ,9x8, 9x9). The 9x9 box also
has 9 rows and 9 columns and each row and each column can hold
numbers from 1 to 9 without repeating. When all squares are filled the
puzzle is solved and the play time is recorded.