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 

chicago tribune 3/2/18 DS too hard - UR help

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



Joined: 19 Jun 2006
Posts: 30

PostPosted: Sun Mar 04, 2018 11:32 pm    Post subject: chicago tribune 3/2/18 DS too hard - UR help Reply with quote

Folks, immp in particular, I believe the puzzle has two URs on 6 & 9 in R2,5 C1,3 and R2,7 C1,7. I worked on the first one and since there were no other 9s in column 3, I eliminated the 6s but wound up at a contradiction.

Any help appreciated especially if it does not involve chains.

Marty tells me that some superb players use chains, but I am still struggling with patterns.

Code:

+----------------+-------+--------------+
| 29    7    3   | 8 6 5 | 4   29   1   |
| 5689  4    69  | 3 1 2 | 7   689  589 |
| 12568 1256 16  | 7 4 9 | 56  3    258 |
+----------------+-------+--------------+
| 7     3    8   | 6 9 1 | 2   5    4   |
| 1269  1269 169 | 4 5 3 | 19  78   78  |
| 4     19   5   | 2 8 7 | 3   19   6   |
+----------------+-------+--------------+
| 69    8    7   | 5 3 4 | 169 1269 29  |
| 15    15   2   | 9 7 6 | 8   4    3   |
| 3     69   4   | 1 2 8 | 569 679  579 |
+----------------+-------+--------------+

Play this puzzle online at the Daily Sudoku site


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



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon Mar 05, 2018 12:48 am    Post subject: Reply with quote

Quote:
Folks, immp in particular, I believe the puzzle has two URs on 6 & 9 in R2,5 C1,3 and R2,7 C1,7. I worked on the first one and since there were no other 9s in column 3, I eliminated the 6s but wound up at a contradiction.


I don't see a UR in r27c17.

As to the first UR, I think it was an error in logic to remove the 6s from c3 based on only two 9s jn that column. If Keith reads this thread, he could explain that much better than I can.
Back to top
View user's profile Send private message
ZeroAssoluto



Joined: 05 Feb 2017
Posts: 285
Location: Rimini, Italy

PostPosted: Mon Mar 05, 2018 8:10 am    Post subject: Reply with quote

Hi Mike,

I don't see UR too.
One way to solve it is a W-Wing 2,9 in r1c1,r7c9 connected by number 2 in r17c8 and -9 in r7c1.

Ciao Gianni
Back to top
View user's profile Send private message
Aj Dimonios



Joined: 01 May 2017
Posts: 324
Location: Sassari Italy

PostPosted: Mon Mar 05, 2018 10:05 am    Post subject: Reply with quote

Hi everyone

[2R1C1-2R1C8=2R7C8-2R7C9 ;(2-9)R1C1=9R1C8-9R6C8=9R6C2-9R9C2=9R7C1-9R7C9]=>contradiction (R7C9=)=>-2R1C1=>solution.


Ciao a Tutti
Paolo
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 326

PostPosted: Mon Mar 05, 2018 4:15 pm    Post subject: Reply with quote

(9=2)r7c9-r7c8=r1c8-(2=9)r1c1=>r7c1<>9
Back to top
View user's profile Send private message
immpy



Joined: 06 May 2017
Posts: 186

PostPosted: Mon Mar 05, 2018 5:49 pm    Post subject: Reply with quote

Mike, the first UR you mentioned is vague, at best. As a Type 4 (and that is stretching the concept, indeed) one could make an elimination of the 9 in both r2c1 and r5c1. But this takes us no further along really, kind of fruitless. There are still too many 9s left to deal with.
The second one you mention I do not see at all. It's not there.

Just curious Mike...are you on a mission with URs?? LOL
You seem to be obsessed with them.
I'm not trying to be critical, or bash, or anything of the sort. Just wondering is all.
I always appreciate any comments and will try to help when I can.

cheers...imp

...and the correct logic would be to eliminate the 9s from the cells opposite of the two cells where 9 is occurring only twice in that house. The 6s should not be removed from anywhere in the UR.

There is a good explanation of the various Uniqueness Tests here:
http://hodoku.sourceforge.net/en/techniques.php

The site goes down for maintenance frequently, it seems, but when it is available it explains things quite well, I find.
Back to top
View user's profile Send private message
mtharp



Joined: 19 Jun 2006
Posts: 30

PostPosted: Mon Mar 05, 2018 7:54 pm    Post subject: Reply with quote

Marty, Gianni & immp, I miss wrote the second one. I see one on 6 & 9 in R2,7 C 1,8 not C 1,7.

immp, I work the Chicago Tribune Friday sudoku - they are the one that keep coming up with them. I am just learning the concept, so I keep asking the questions. I appreciate your patience with me.

Everyone thank you.

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



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Mon Mar 05, 2018 10:06 pm    Post subject: Reply with quote

With all the UR talk here, has everyone read Keith's article on the basics?

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=3578
Back to top
View user's profile Send private message
immpy



Joined: 06 May 2017
Posts: 186

PostPosted: Tue Mar 06, 2018 5:58 am    Post subject: Reply with quote

Upon a closer look and a refresher of the concepts of URs, I would not even designate either of these as a UR of known type (the possible two 69 URs that Mike is referring to). I did see the second one you were referring to Mike, after your correction of the earlier post.
There are simply too many 6s and 9s in the houses (rows, columns, and boxes) that make up these rectangles in order for them to be present. And any extra candidates present do not seem to form a pseudo-cell with other candidates in a common house (row, column, or box).

I think the W-wing is the way to go here, as Gianni pointed out.
Back to top
View user's profile Send private message
immpy



Joined: 06 May 2017
Posts: 186

PostPosted: Tue Mar 06, 2018 6:20 am    Post subject: Reply with quote

Thanks for the link to Keith's article Marty, that is some good reading there.
More for our brains to try and wrap around.
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Tue Mar 06, 2018 1:29 pm    Post subject: Reply with quote

Just my personal practice; when the potential UR has too many candidates to qualify as a Type X, I refer to it as a DP.
Back to top
View user's profile Send private message
mtharp



Joined: 19 Jun 2006
Posts: 30

PostPosted: Wed Mar 07, 2018 3:11 am    Post subject: Reply with quote

Marty, as per immp, thanks for the link to Keith's tutorial. Enlightening.

Showing my ignorance, I have to ask, what is DP (unless it refers to the pornographic term).

I am now reading up on W wings. Hope I do not bother you folks with too many questions.

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



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Wed Mar 07, 2018 4:37 pm    Post subject: Reply with quote

Quote:
Showing my ignorance, I have to ask, what is DP (unless it refers to the pornographic term).


Not ??. DP =Deadly Pattern any pattern from URs to a full BUG where two solutions can be found due to bivalue cells reversing.
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