Sudoku solver

[Chris Angelico]

On Thu, Mar 26, 2015 at 11:26 PM, Marko Rauhamaa <marko at pacujo.net> wrote:
> "Frank Millman" <frank at chagford.com>:
>
>> Here is another python-based sudoku solver -
>>
>> http://www.ics.uci.edu/~eppstein/PADS/Sudoku.py
>>
>>>From its docstring -
>>
>> "A proper Sudoku puzzle must have a unique solution, and it should be
>> possible to reach that solution by a sequence of logical deductions
>> without trial and error.
>
> I don't think that statement holds water. Trial-and-error is at the
> basis of deduction (reductio ad absurdum). The human solver employs it
> in their head. The question is, what is the difference between
> pen-and-paper and in-your-head for a computer program?

Nothing. And solving a Sudoku puzzle - or any other puzzle - should
require no guessing. It should be possible to solve purely by logic.
Same goes for every other kind of puzzle out there; it's highly
unsatisfying to play Minesweeper and get to the end with a block of
four squares in a corner, two mines left, and no way of knowing which
diagonal has the mines and which is clear.

No trial-and-error, thanks.

ChrisA