Sorry, al the comments are in italian.
The file with the code is SudokuSolvabe.java.
This is not serious, every contribution is good.
TODO:
- comments
- convert all the squares in a functional programming code(there are two nested for that perform the same operation in all the little squares of the sudoku, these loops are present in more than one method, using lambda instead would be great)
- add new solving tecniques(es. xwing, couple on the same line/column/square...)