Mastering Sudoku Puzzle #15

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Mastering Sudoku Puzzle #15

Postby dummy » Thu Apr 17, 2008 8:06 pm

(I know, I know! I haven't been able to contact the author)

Does anyone here have a copy of "Mastering Sudoku" and can help me with puzzle #15? I can type it in if necessary. The exercise is on pairs, and I just don't understand the concept. Sometimes there are only two candidates, sometimes more, and there seem to be a variety of things you can do with the information gained. I need a reference with many, many examples, not yet another treatise with a few ill-defined rules.

Specifically, in the partially solved puzzle #15 on page 71, there's supposed to be a pair that "leads to a long chain of solved squares". I find a couple of redundant pairs, and another pair that eliminates a 2 from cell r9 c1, but I can't see how that helps.

Thanks
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Re: Mastering Sudoku Puzzle #15

Postby Cec » Fri Apr 18, 2008 11:18 am

dummy wrote:"...Does anyone here have a copy of "Mastering Sudoku" and can help me with puzzle #15? I can type it in if necessary....

dummy, if you want to be helped you need to post the original puzzle and the stage you reached. Click on HERE for posting procedures.

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Postby dummy » Fri Apr 18, 2008 2:41 pm

The original puzzle:

Code: Select all
 . . 5 | . 2 . | . 1 .
 6 . . | 5 . . | 7 . 8
 . 2 . | 1 . . | . . 5
-------+-------+-------
 . . 3 | 9 8 . | 4 . .
 . . 4 | . . . | 8 . .
 . . 9 | . 7 5 | 1 . .
-------+-------+-------
 5 . . | . . 7 | . 8 .
 1 . 8 | . . 9 | . . 6
 . 7 . | . 4 . | 5 . .


This is where things stop:

Code: Select all
 4 . 5 | 7 2 . | . 1 .
 6 . 1 | 5 . 4 | 7 2 8
 . 2 7 | 1 . . | . 4 5
-------+-------+-------
 . . 3 | 9 8 . | 4 . .
 . . 4 | . . . | 8 . .
 . . 9 | 4 7 5 | 1 . .
-------+-------+-------
 5 . . | . 1 7 | . 8 4
 1 4 8 | . 5 9 | . 7 6
 . 7 . | . 4 . | 5 . 1


Same as above, with candidates:

Code: Select all
 4   389 5  | 7    2   368  | 369 1    39
 6   39  1  | 5    39  4    | 7   2    8
 389 2   7  | 1    369 368  | 369 4    5
------------+---------------+---------------
 27  156 3  | 9    8   126  | 4   56   27
 27  156 4  | 236  36  1236 | 8   3569 2379
 28  68  9  | 4    7   5    | 1   36   23
------------+---------------+---------------
 5   369 26 | 236  1   7    | 239 8    4
 1   4   8  | 23   5   9    | 23  7    6
 239 7   26 | 2368 4   2368 | 5   39   1


As I said, I find the redundant pairs in column 3 and row 2,

and the 2's claim eliminates a candidate 2 from cell r9c1,

but I don't see how this helps.
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Postby daj95376 » Fri Apr 18, 2008 3:23 pm

The 8 in column 4 doesn't help much, either. How about the pair in column 1:?:
Last edited by daj95376 on Fri Apr 18, 2008 11:24 am, edited 1 time in total.
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Mastering Sudoku Puzzle #15

Postby Cec » Fri Apr 18, 2008 3:24 pm

Post withdrawn. daj95376 you pipped me by one minute:)

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Postby dummy » Fri Apr 18, 2008 4:55 pm

daj95376 wrote:The 8 in column 4 doesn't help much, either. How about the pair in column 1:?:


I guess that's my problem: I'm not sure what a valid pair looks like in all situations. If you're talking about the 27 pair in r1c4 and r1c5, I thought there could not be any other 2's or 7's in the group. But now that I look at it again, I think the 27 pair would eliminate the 2 in r1c6, leaving an 8 single candidate. Is that right?
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Postby dummy » Fri Apr 18, 2008 5:47 pm

(Replying to myself)

Yep, that did it: everything fell to single candidates after that.

Thanks:!:

I learned two things: naked pairs, and to look for single candidates in rows and colums as well as boxes.
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Mastering Sudoku Puzzle #15

Postby Cec » Sat Apr 19, 2008 12:08 am

dummy wrote:"....Thanks:!:

I learned two things: naked pairs, and to look for single candidates in rows and colums as well as boxes."


And thank you dummy for your appreciating getting help... so much more refreshing when newcomers respond to let us know you understood the help offered and then able to solve your puzzle.

In addition to naked pairs and singles, there are other basic solving techniques which you can read up on by clicking on the following links.....

http://www.angusj.com/sudoku/hints.php
http://www.sadmansoftware.com/sudoku/techniques.htm
http://www.scanraid.com/BasicStrategies.htm

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Postby Pat » Mon Apr 21, 2008 7:20 am

dummy wrote:
Code: Select all
 . . 5 | . 2 . | . 1 .
 6 . . | 5 . . | 7 . 8
 . 2 . | 1 . . | . . 5
-------+-------+-------
 . . 3 | 9 8 . | 4 . .
 . . 4 | . . . | 8 . .
 . . 9 | . 7 5 | 1 . .
-------+-------+-------
 5 . . | . . 7 | . 8 .
 1 . 8 | . . 9 | . . 6
 . 7 . | . 4 . | 5 . .




in box 4,
the {1,5} have only 2 cells available
    this solves the 6 for that box
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