dailysudoku.com Forum Index dailysudoku.com
Discussion of Daily Sudoku puzzles
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

jan 24 puzzle

 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Other puzzles
View previous topic :: View next topic  
Author Message
bernard
Guest





PostPosted: Wed Jan 25, 2006 9:20 am    Post subject: jan 24 puzzle Reply with quote

hi, i m stuck after 25 moves. who can help ?
Back to top
David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Wed Jan 25, 2006 12:24 pm    Post subject: I need more information ... Reply with quote

Hi, Bernard!

I can probably help you. But I need to know exactly where you got stuck. There are a whole lot of different ways to make 25 moves on a sudoku!

Please post your position. dcb
Back to top
View user's profile Send private message Send e-mail Visit poster's website
bernard
Guest





PostPosted: Wed Jan 25, 2006 4:03 pm    Post subject: my position Reply with quote

9.5 .76 4..
3.6 ... 597
.47 ..9 ..6

572 6.8 .41
16. .47 ..5
4.. 1.5 67.

65. 7.3 124
731 ... 869
..4 .61 753

thank u for help
Back to top
David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Wed Jan 25, 2006 7:34 pm    Post subject: This is a "Nightmare", Bernard Reply with quote

Hi again, Bernard. I got confused because you were talking about one of Ruud's "Nightmare" puzzles -- I thought you were asking about a puzzle from Samgj's Daily Sudoku site!

Anyway, at the point you've reached the matrix of possibilities looks like this.
Code:
 9  128  5  238   7    6   4  138 28
 3  128  6  248  128  24   5   9   7
28   4   7 2358 12358  9  23  138  6
 5   7   2   6   39    8  39   4   1
 1   6  389 239   4    7  239 38   5
 4  89  389  1   239   5   6   7  28
 6   5  89   7   89    3   1   2   4
 7   3   1  245  25   24   8   6   9
28  289  4  89    6    1   7   5   3

Let's concentrate on r7c5, where the {8, 9} pair is possible. And let's assume that r7c5 = 9. We derive a contradiction pretty quickly, as follows.

r7c5 = 9 ==> r7c3 = 8 ==> {3, 9} pair in r5c3 & r6c3
r7c5 = 9 ==> r4c5 = 3 ==> r6c5 = 2 ==> r6c9 = 8 ==> r6c2 = 9

But now we've reached a contradiction, because there's no way to fit an "8" in the center left 3x3 box. So r7c5 <> 9, and we must have r7c5 = 8. With this one additional value set you should be able to complete the puzzle. dcb

PS In an earlier post I said there were two closely related forcing chains in the puzzle, but I was wrong -- this one chain at r7c5 is enough to do the trick.
Back to top
View user's profile Send private message Send e-mail Visit poster's website
bernard



Joined: 25 Jan 2006
Posts: 1
Location: france

PostPosted: Thu Jan 26, 2006 2:45 pm    Post subject: Reply with quote

Smile Smile thank u for this chain I hadn't found
________
Ford Fiesta RS Turbo specifications


Last edited by bernard on Mon Jan 31, 2011 6:34 pm; edited 1 time in total
Back to top
View user's profile Send private message
David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Thu Jan 26, 2006 5:19 pm    Post subject: There's another to view the same formation Reply with quote

You're welcome, Bernard.

Looking at this again, I notice another way of viewing it that may seem more intuitive ...
Code:
 9  128  5  238   7    6   4  138 28
 3  128  6  248  128  24   5   9   7
28   4   7 2358 12358  9  23  138  6
 5   7   2   6   39    8  39   4   1
 1   6  389 239   4    7  239 38   5
 4  89  389  1   239   5   6   7  28
 6   5  89   7   89    3   1   2   4
 7   3   1  245  25   24   8   6   9
28  289  4  89    6    1   7   5   3

Think about what will happen if r6c2 = 8. This will change the {3, 8, 9} in r5c3 & r6c3 into a {3, 9} pair, forcing an "8" at r7c3.

But r6c2 = 8 also forces r6c9 = 2, which creates the {3, 9} pair in r4c5 & r6c5, forcing an "8" at r7c5. But we can't have two "8"s in row 7, so r6c2 = 9.

It's a cute pattern. dcb
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Other puzzles All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group