Sudoku

The grid is of 9 by 9 spaces. In the rows and columns there are 9 squares which are made of 3 by 3 spaces.
Game rules are that in each row, column and square needs to be filled out with the numbers from 1 to 9, without repeating any numbers within the row, column or square.
The app does collect user data, all the data is saved only on the mobile device.