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Are Advanced Techniques Necessary?

 
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Andie

Joined: 03 Oct 2005
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PostPosted: Mon Oct 03, 2005 3:31 pm    Post subject: Are Advanced Techniques Necessary? Reply with quote

I understand that all Sudoku puzzles have one solution only. I solve them by elimination and have done well until now. Are some of the most difficult puzzles solvable only by an if/then process? Thanks
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Ruud
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Joined: 17 Sep 2005
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PostPosted: Tue Oct 04, 2005 1:10 am    Post subject: Reply with quote

Please try this puzzle (it does have a unique solution)

Code:
. . .|. . .|. 1 4
. . .|. . .|2 . 3
8 . .|. 5 .|. . .
-----+-----+-----
. . .|2 . 7|. . .
. 3 1|. . .|. . .
. . .|. . .|6 5 .
-----+-----+-----
6 . .|. . .|7 . .
. . .|1 4 .|. . .
. . .|3 . .|. . .

It might change your opinion...

To view the solution, select the area below *** SPOILER ***
7 6 9|8 2 3|5 1 4
1 4 5|7 6 9|2 8 3
8 2 3|4 5 1|9 7 6
-----+-----+-----
4 5 6|2 1 7|3 9 8
9 3 1|6 8 5|4 2 7
2 7 8|9 3 4|6 5 1
-----+-----+-----
6 1 4|5 9 8|7 3 2
3 9 7|1 4 2|8 6 5
5 8 2|3 7 6|1 4 9
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Andie

Joined: 03 Oct 2005
Posts: 2
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Location: Southern California

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PostPosted: Tue Oct 04, 2005 3:00 am    Post subject: Reply with quote

[quote="Ruud"]Please try this puzzle (it does have a unique solution)

Code:
. . .|. . .|. 1 4
. . .|. . .|2 . 3
8 . .|. 5 .|. . .
-----+-----+-----
. . .|2 . 7|. . .
. 3 1|. . .|. . .
. . .|. . .|6 5 .
-----+-----+-----
6 . .|. . .|7 . .
. . .|1 4 .|. . .
. . .|3 . .|. . .

It might change your opinion...

Hi Ruud,

I tried the puzzle and it looks like a mess. Using the basic techniques I added the following numbers:

5 in r1c7
8 in r2c8
9 in r3c7
7 in r9c5
4 in r3c4

I don't know any of the advanced techniques, but I don't like guessing or using an if/then logic. I'll just stick to the easier puzzles! Thanks for your answer. I really like your hidden solution....very cool!
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gaby

Joined: 02 Jul 2005
Posts: 120
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PostPosted: Wed Oct 05, 2005 8:09 pm    Post subject: Reply with quote

That's an impressively difficult puzzle! Where did you get it from? I managed to break it with templates, but there's a nice sequence of methods that are applied to get there Smile
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Ruud
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PostPosted: Thu Oct 06, 2005 12:03 am    Post subject: Reply with quote

You can find more than 24000 sudoku with 17 clues on this site.

It's a big file to download, but amongst many easy to solve sudokus are a few real gems. This was one of them.
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qbasicmac

Joined: 26 Jul 2005
Posts: 27
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Location: Washington DC

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PostPosted: Thu Oct 06, 2005 2:02 am    Post subject: Reply with quote

Couldn't find "spoiler". Had to do it the hard way Sad

769 823 514
145 769 283
823 451 976
456 217 398
931 685 427
278 934 651
614 598 732
397 142 865
582 376 149
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Ruud
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PostPosted: Thu Oct 06, 2005 2:49 am    Post subject: Reply with quote

There is no real spoiler tag. Just set the font color to the back color. Beware that the posts have alternating back colors.
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qbasicmac

Joined: 26 Jul 2005
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PostPosted: Thu Oct 06, 2005 12:24 pm    Post subject: Reply with quote

Thanks for the info, Ruud

Interesting. Would never have guessed that.

Mac
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Lummox JR

Joined: 07 Sep 2005
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PostPosted: Sat Oct 08, 2005 2:35 am    Post subject: Reply with quote

I found multicoloring cracked that puzzle pretty nicely, but with 40 colors (20 conjugate pairs) in the initial setup it's an awful lot to figure out. Manually calculating transitivity among the exclusions for that many colors can get pretty hairy.
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qbasicmac

Joined: 26 Jul 2005
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PostPosted: Sun Oct 09, 2005 2:42 am    Post subject: Reply with quote

Say, Ruud,

Something I am curious about. I see in your SPOILER technique the same thing I note in newspapers. The solution is considered some kind of secret to be published tomorrow or set at the back of the book.

I can understand that for crossword puzzles, because seeing the answer gives it away.

But in SuDoku, any junior programmer can write a program that will solve puzzles and many have been posted. Anyway, who cares what the answer is? The question is how to get there.

I could live in a world where SuDoku puzzles and their solutions are always posted side by side. Wouldn't reduce the challenge one iota.

So anyway, I just wonder what the big secrecy deal is.

Mac

P.S. Maybe I just have an abnormal mind. I also like to tape football games and only watch them after I know the result so I don't get too excited. I already know we won or lost, but am still curious to know how it happened.
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Ruud
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PostPosted: Sun Oct 09, 2005 10:09 am    Post subject: Reply with quote

Well Mac,
not all people have a scientific approach to Sudoku like you do. In math and physics, you often get an equasion and you have to prove that the answer is correct.

In Sudoku however, taking away the fun of discovering the solution, because the answer is staring them in the face all the time, would not appeal to many Sudokorists.

The Sudoku that appear in newspapers and books usually do not require many advanced techniques, so the searching becomes more important than the proving. When a puzzle requires more advanced techniques, there is less emphasis on the search, though you still need to find and recognize the patterns that you can use in these techniques.

Solving a Sudoku using a computer program can be done without the solution. When you have completed the grid and did not violate the rule (which most programs do not allow) you already have the solution.
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