Game Sudoku Challenge

If you like the great challenges, you have in front of you one of the most complicated solitaires there is, the Sudoku. You have to fill in the boxes that are empty, you know, you can not repeat numbers in the same row, in the same column, or in the same grid of 9 boxes. Before starting to play, you have to choose at what level you want to do it, it is easier is Hard ...