Sudoku

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Are these puzzles banned here? I got this one in an AA mag and I am pretty sure that you need to solve it by trial and error – I hate that, give me logic or give me death.

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Why should they be banned?

Solving a Sudoku puzzle is usually a mixture of logical reasoning and guessing…
Don Wells posted a sudoku solver a few years ago, but it was lost in the server crash of last year.

Added later: I found it in my archive – I’ve attached the zip file. I’m aware it’s not the “logic” your seeking.

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I thought you would get so many of these that you would get sick of them. I ran the solver and it solved it – true to its name. I looked at the code and it included a ‘guess’ routine. Disabling the guess routine gave a partial solution that is less solved than I got on my own (see below for where I am stuck).

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I don’t think you can solve Sudoku puzzles solely by logical thinking, except perhaps for very simple ones (where you’re given a lot of information). You can get only so far by reasoning, then you’ll have to guess and try to continue reasoning from there, etc. If you find a contradiction, you’ll have to backtrack and try again.

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I don’t 100% agree with that statement. For me, the ‘better’ sudoku puzzles are ones that you can solve with logic, coupled with some ‘estimates that lead to inconsistencies’. I don’t mind those as long as they are only 3 or 4 chains long (ie you can do it in your head.

Take the ‘6’ in the top middle big square … that has to be a 6 because …

1) the middle / middle big square’s 6 must be in the center column, thus ruling out the center column for the top middle square
2) the 6 in the top left big square rules out the 2nd row in the top middle big square
3) the 6 mentioned in 2) also forces the 6 in the top left big square to the top row, thus ruling out the top row in the top middle big square

I know that I can solve this puzzle by ‘guessing’ the value of 1 square (it is either a 3 or a 9), but if I put a 3 in that square, it requires 15 or so passes to come to an inconsistency. Not something that I can do in my head. I guess I don’t want to fall back on the (as my prof use to say) ‘brute force and stupidity’ method.

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There seems to be a logic to it to me. Much like an IF … THEN or IF … ELSE … THEN or similar in various programming languages. I know in the simpler puzzles, the “it has to be this” is very easy to determine, but as they get harder, I switch from a case of “This square is X” to “This square can not be X,Y, or Z”.

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