As far as I know an ordinary 9x9 sudoku must initially have 17 clues minimun. Can theese 17 clues be in any position (even if that means to have an empty row or column)? Or must it be at least 1 clue per row and column?
I have no idea on how to find the answer so it would be great if anybody knew it or knew some method I can use to find it. Thanks in advance.
I think it's possible with an empty row/column, I just clicked through some examples and found the following sudoku: http://sudoku99.com/sudoku9x9/20_level_17_hint/?722581
I checked and it's indeed a solvable sudoku. Hope this helps :)