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 

LA Times / Freep 4 April, 2008

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



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 05, 2008 11:43 am    Post subject: LA Times / Freep 4 April, 2008 Reply with quote
Any creative ideas?
Code:
Puzzle: FP040408
+-------+-------+-------+
| 2 . . | . 4 . | . . 5 |
| . . . | 5 . . | . 7 . |
| . 5 . | . . 1 | . 3 . |
+-------+-------+-------+
| . . 7 | 8 1 . | 6 . . |
| . . 9 | . 5 . | 2 . . |
| . . 1 | . 3 2 | 7 . . |
+-------+-------+-------+
| . 9 . | 4 . . | . 1 . |
| . 6 . | . . 5 | . . . |
| 8 . . | . 6 . | . . 7 |
+-------+-------+-------+

Keith
Back to top
View user's profile Send private message
Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
PostPosted: Sat Apr 05, 2008 12:57 pm    Post subject: Reply with quote
Code:
+----------------------------------------+
| 2    7   8   | 3   4   9  | 1   6   5  |
| 1349 134 346 | 5   28  68 | 48  7   29 |
| 49   5   46  | 267 278 1  | 48  3   29 |
------------------------------------------
| 5    2   7   | 8   1   4  | 6   9   3  |
| 34   348 9   | 67  5   67 | 2   48  1  |
| 6    48  1   | 9   3   2  | 7   5   48 |
------------------------------------------
| 37   9   23  | 4   278 78 | 5   1   6  |
| 17   6   34  | 17  9   5  | 3   248 48 |
| 8    14  5   | 12  6   3  | 9   24  7  |
+----------------------------------------+


You can use a generalised XY-wing with pivot r78c1. These two cells must contain 1 or 3, just like a bivalent cell (13). The pincers r5c1 and r9c2 then eliminate 4 from r56c2.

Steve
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 05, 2008 1:27 pm    Post subject: Reply with quote
Really?

It seems correct, but I do not recall seeing this before!

In Steve's grid there is a skyscraper that takes out <4> in R8C9, but that does not solve the puzzle. It gets you here:
Code:
+----------------+----------------+----------------+
| 2    7    8    | 3    4    9    | 1    6    5    |
| 1349 134  346  | 5    28   68   | 48   7    29   |
| 49   5    46   | 267  278  1    | 48   3    29   |
+----------------+----------------+----------------+
| 5    2    7    | 8    1    4    | 6    9    3    |
|-34   34#  9    | 67   5    67   | 2    8    1    |
| 6    8    1    | 9    3    2    | 7    5    4    |
+----------------+----------------+----------------+
| 37#  9    23   | 4    278  78   | 5    1    6    |
| 17@  6    24   | 17   9    5    | 3    24   8    |
| 8    14@  5    | 12   6    3    | 9    24   7    |
+----------------+----------------+----------------+

Can I make this similar argument: Question
R8C1 and R9C2 , @, must contain one of <47>.
Either way, one of the pincer cells # is <3>, and we can take out <3> in R5C1. Surprised

(I do see that there are short chains that solve R5C12. I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4.)

Keith

Last edited by keith on Sat Apr 05, 2008 5:21 pm; edited 1 time in total
Back to top
View user's profile Send private message
Victor



Joined: 29 Sep 2005
Posts: 207
Location: NI
PostPosted: Sat Apr 05, 2008 4:48 pm    Post subject: Reply with quote
And, not as exciting as Steve's stuff, the ER based on r9 takes out the 4 in r6c2, exposing a type 4 in 34s in r2c12. Same effect as Keith's skys, I guess - still a little work to do.
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Apr 05, 2008 5:11 pm    Post subject: Reply with quote
Quote:
I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4

Keith, Medusa will color the 1 in r2c2 as "A." The 1 and 3 in r2c1 and r2c3, respectively, will be colored "B." Thus the 4 in r2c2 will be "B", eliminating the 3 and exposing a 14 pair in column 2.
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 05, 2008 6:42 pm    Post subject: Reply with quote
Marty R. wrote:
Quote:
I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4

Keith, Medusa will color the 1 in r2c2 as "A." The 1 and 3 in r2c1 and r2c3, respectively, will be colored "B." Thus the 4 in r2c2 will be "B", eliminating the 3 and exposing a 14 pair in column 2.

Marty,

Thanks. I did not take it that far. I confined my search to B47 in the hopes of finding a short chain like Steve did.

Keith
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Apr 05, 2008 10:48 pm    Post subject: Reply with quote
Put in my two cents:

http://www.sudoku.com/boards/viewtopic.php?p=54708#54708

Keith
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun Apr 06, 2008 12:11 am    Post subject: Reply with quote
From that other forum:

Quote:
These turn out to be 4-link XY-chains. As Steve observed, sort of an extended XY-wing.


Ah, but as Steve described it, a "generalized XY-Wing" has more status and, to use a word often seen here, much more elegant than an XY-Chain. Laughing
Back to top
View user's profile Send private message
tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
PostPosted: Sun Apr 06, 2008 1:33 am    Post subject: Reply with quote
I used multi-coloring to remove <4> from r5c8, r6c2 & r8c9. If I then use the "generalized XY-wing with pivot r78c1" noted by Steve, the puzzle is completed.

Steve, is your generalized solution a valid technique?

Ted
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sun Apr 06, 2008 2:29 am    Post subject: Reply with quote
Marty R. wrote:
From that other forum:

Quote:
These turn out to be 4-link XY-chains. As Steve observed, sort of an extended XY-wing.


Ah, but as Steve described it, a "generalized XY-Wing" has more status and, to use a word often seen here, much more elegant than an XY-Chain. Laughing


Marty,

This is new to you?

Keith
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun Apr 06, 2008 3:50 am    Post subject: Reply with quote
Quote:
This is new to you?


Yes, if you mean the generalized XY-Wing, no if you mean XY-Chains.
Back to top
View user's profile Send private message
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