Forward solve Boston Globe from Jan 21, 2006?

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Forward solve Boston Globe from Jan 21, 2006?

Postby eclectic_mix » Mon Jan 23, 2006 4:19 pm

While I was able to solve the Sudoku from Saturday's Globe, I was not able to solve it with only forward solving techniques. A friend has a solving program using only forward solving algorithms and it failed to solve this puzzle as well.

Here's the puzzle:

.2......3
..78.....
63.5...8.
..2.4...8
..5.2.9..
4...5.7..
.9...6.31
.....56..
1......9.

I eventually needed to take a guess to solve this puzzle at which point I was able to complete it successfully. Can anyone solve this using only forward solving methods and no guessing?

Thanks!
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Postby Carcul » Mon Jan 23, 2006 4:34 pm

Hi Eclectic_mix.

Honestly, I don't know what is the problem with this puzzle: the "harder" step it requires is a hidden pair in cells r8c4/r8c5. From here, there are only naked and hidden singles.

Regards, Carcul
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Postby tarek » Mon Jan 23, 2006 4:54 pm

I would be surprised to know that a solver program would not solve this. I can understand a person getting stuck at a point in the puzzle above, but for a program !!!!

I would suggest abandoning that solver altogether.
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Thanks...

Postby eclectic_mix » Mon Jan 23, 2006 5:13 pm

I'm going to go back and resolve the puzzle to see if I run into the same stumbling block. I don't frequently go back and resolve puzzles but when the program couldn't solve it forward, I figured I would ask here. Now that I know you've solved it forward, I'll try again and pass along your comments to the programmer.

The solver is a forward solver. It attempts to only use the same logic humans would without resorting to any guessing or exhaustive searching. It's possible the programmer may have missed an element of forward solving algorithms and would want to modify the program accordingly.

Any solver (human or computer) that includes any form of searching or guessing would be able to solve this puzzle easily.

Thanks for your input.
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yeah, it forward solves quite easily {on second attempt ;-}

Postby eclectic_mix » Mon Jan 23, 2006 5:51 pm

Amazing how the brain works. I realized quite early on that I was solving this puzzle in quite a different order than during my first attempt and it went quite easily. The hidden pairs hint never even came into play as it wasn't all that hidden. When I filled in the cell that had been my "guessing" cell the first time around and I filled it in quite early, I knew it was going to "go" this time.

Anyway, I'll be passing along this info to the programmer.

FWIW, I'm not sure he created the solver to solve puzzles so much as to prove some sort of math problem. He's a friend of a couple of friends of mine and my friends are all math gurus from MIT. Anyway, I think he's got some tweaking to do.

Thanks again.
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