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 

recommended: today's nightmare

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



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Thu Dec 13, 2007 9:10 am    Post subject: recommended: today's nightmare Reply with quote

Today's Daily Nightmare once more turned out to be a very satisfying puzzle.

xy-wing and x-wing got me here:

Code:

+--------------------------+--------------------------+--------------------------+
| 58      135     18       | 24      359     7        | 89      6       24       |
| 679     37      2        | 46      36      8        | 1       5       49       |
| 4       59      689      | 1       569     25       | 7       3       28       |
+--------------------------+--------------------------+--------------------------+
| 2       6       3        | 8       1       9        | 4       7       5        |
| 1       457     47       | 57      2       3        | 89      89      6        |
| 58      579     789      | 57      4       6        | 3       2       1        |
+--------------------------+--------------------------+--------------------------+
| 3       8       19       | 26      56      4        | 25      19      7        |
| 79      2       5        | 3       78      1        | 6       4       89       |
| 67      147     1467     | 9       78      25       | 25      18      3        |
+--------------------------+--------------------------+--------------------------+


I see at least two different solution paths now:
A) potential DP (57) r56c24 => r5c2=4 or r6c2=9, both lead to r5c4=5.
B) xy-chain *): (9)r7c3 ... [useless xy-wing 91-18-89 + transport to] ... (9)r5c8 makes r7c8=1

edit: *) xy-chain ? or w-wing ? M-wing ? wingding ? Laughing
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Thu Dec 13, 2007 5:59 pm    Post subject: Nightmare Reply with quote

There is a w-wing 18 apparently elliminating nothing, but if you color the lower pincer 8 to R3C9 that makes R1C7 = 9 and the puzzle is solved.

Earl
Back to top
View user's profile Send private message Send e-mail
nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Thu Dec 13, 2007 6:41 pm    Post subject: Reply with quote

I'll add that to the list of powerful chains based on apperently useless wings.

So far, we have:

(9)r7c3 19-18-89-89-89 (9)r5c8 ; r7c8=1 (nataraj's)
(8)r1c3 18-19-19-18-89-49-24-28 (8)r3c9; R1C7 = 9 (Earl's)

If we start with the same useless w-wing but continue up and left we get to r5c7 with the same result

(8)r1c3 18-19-19-18-89-89 (8)r5c7 ; r1c7=9 (Earl's II)

and here's one more, it removes 1 from r7c3. It looks like a normal xy-wing but with an extension cord added in the middle:

(1)r1c3 18-89-89-89-19 (1)r7c8 ; r7c3=9
Back to top
View user's profile Send private message Send e-mail Visit poster's website
keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Thu Dec 13, 2007 11:11 pm    Post subject: Reply with quote

nataraj wrote:
I'll add that to the list of powerful chains based on apparently useless wings.



Flightless wings?

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



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Fri Dec 14, 2007 12:32 am    Post subject: Reply with quote

Ostrich?
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Fri Dec 14, 2007 5:55 am    Post subject: Reply with quote

Some might have noticed I have been intrigued recently with otherwise useless X-Wings involved with overlapping strong links. In this case, I saw the <4> X-Wing in Boxes 2 and 3 with the overlapping <2> strong link in r1. Together with the Box 2 strongly linked <2>s and several related bivalues, I thought: Medusa! I usually don't resort to Medusa so soon. But, this seemed so promising:
Code:
+--------------+-----------------+--------------+
| 58  135 18   | 2r4g  359r 7    | 8r9g 6  2g4r |
| 679 37  2    | 4r6g  3-6  8    | 1    5  4g9r |
| 4   59  689  | 1    -569g 2g5r | 7    3  2r8g |
+--------------+-----------------+--------------+
| 2   6   3    | 8     1    9    | 4    7  5    |
| 1   457 47   | 57    2    3    | 89   89 6    |
| 58  579 789  | 57    4    6    | 3    2  1    |
+--------------+-----------------+--------------+
| 3   8   19   | 26    56   4    | 25   19 7    |
| 79  2   5    | 3     78   1    | 6    4  89   |
| 67  147 1467 | 9     78   25   | 25   18 3    |
+--------------+-----------------+--------------+

Very easily, <5> is eliminated from r3c5. (It contains a green <9> and sees a red <5>.) This makes the <6> in r3c5 red, eliminating <6> from r2c5 and solving the puzzle.
Back to top
View user's profile Send private message Visit poster's website
nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Fri Dec 14, 2007 6:40 am    Post subject: Reply with quote

TKiel wrote:
Ostrich?


Laughing That's it! Let's call it ostrich wing (or O-wing for short). Nobody's going to believe this... Laughing
Back to top
View user's profile Send private message Send e-mail Visit poster's website
storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Fri Dec 14, 2007 7:29 am    Post subject: Reply with quote

are we "o-wing" you anything for this?
Back to top
View user's profile Send private message
nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Fri Dec 14, 2007 7:42 am    Post subject: Reply with quote

it was a collaboration - but "ostrich" was suggested by Tracy, to be sure.


I can think of many more uses for the name. Take those solution methods, for example, that leave me with my mouth open ... :-O oooohhh - wing!
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