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 

Aug 9 VH

 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku puzzles
View previous topic :: View next topic  
Author Message
hughwill



Joined: 05 Apr 2010
Posts: 424
Location: Birmingham UK

PostPosted: Sun Aug 09, 2015 11:13 am    Post subject: Aug 9 VH Reply with quote

After basics:
Code:

+------------+-----------+---------+
| 18 178 68  | 57 457 29 | 29 3 46 |
| 5  23  4   | 39 8   6  | 29 7 1  |
| 9  237 236 | 1  47  23 | 8  5 46 |
+------------+-----------+---------+
| 4  6   5   | 8  9   7  | 1  2 3  |
| 2  9   1   | 6  3   5  | 4  8 7  |
| 7  38  38  | 2  1   4  | 6  9 5  |
+------------+-----------+---------+
| 38 4   89  | 39 57  1  | 57 6 2  |
| 6  5   7   | 4  2   8  | 3  1 9  |
| 13 12  29  | 57 6   39 | 57 4 8  |
+------------+-----------+---------+

Play this puzzle online at the Daily Sudoku site
Took me a very long time to see the simple
Quote:
392 XY-wing pivot r9c6
which solves it.

Hugh
(fra Stavanger i dag)
Back to top
View user's profile Send private message
bat999



Joined: 09 Jul 2015
Posts: 55
Location: UK

PostPosted: Sun Aug 09, 2015 12:31 pm    Post subject: Reply with quote

Code:
.------------------.--------------.------------.
| 18   1278   268  |  57  457  29 | 289  3  46 |
| 5   a23     4    | b39  8    6  | 29   7  1  |
| 9    2378   2368 |  1   47   23 | 28   5  46 |
:------------------+--------------+------------:
| 4    6      5    |  8   9    7  | 1    2  3  |
| 2    9      1    |  6   3    5  | 4    8  7  |
| 7    38     38   |  2   1    4  | 6    9  5  |
:------------------+--------------+------------:
| 38   4     d89   | c39  57   1  | 57   6  2  |
| 6    5      7    |  4   2    8  | 3    1  9  |
| 13   1-2   e29   |  57  6    39 | 57   4  8  |
'------------------'--------------'------------'
(2=3)r2c2 - (3=9)r2c4 - (9)r7c4 = r7c3 - (9=2)r9c3 => -2 r9c2; stte
Cool


Last edited by bat999 on Mon Aug 10, 2015 8:50 pm; edited 1 time in total
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 568

PostPosted: Sun Aug 09, 2015 3:06 pm    Post subject: Reply with quote

Hey! Wait a minute! Hugh's starting grid looks to me like he already applied the two 39-2 XY-wings with pivot at r2c4 to eliminate the 2 from r1c23 and the 2 from r3c7. Did I miss some basic moves that eliminate them?
Back to top
View user's profile Send private message
Marty R.



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

PostPosted: Sun Aug 09, 2015 3:29 pm    Post subject: Reply with quote

dongrave wrote:
Hey! Wait a minute! Hugh's starting grid looks to me like he already applied the two 39-2 XY-wings with pivot at r2c4 to eliminate the 2 from r1c23 and the 2 from r3c7. Did I miss some basic moves that eliminate them?


I saw the grid and thought I screwed up the basics since I had 28 in r3c7 and found that the wing pivoted in r2c4 wasn't enough.
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 568

PostPosted: Sun Aug 09, 2015 7:33 pm    Post subject: Reply with quote

I went back and looked at it again and it looks to me like Bat's grid is right after basics and then in order to solve it using just standard VH moves (i.e. wings), you need to apply at least one of the two 39-2 XY-wings with pivot at r2c4 (either one will do) along with Hugh's XY-wing. Someone let me know if I'm wrong.
Back to top
View user's profile Send private message
hughwill



Joined: 05 Apr 2010
Posts: 424
Location: Birmingham UK

PostPosted: Mon Aug 10, 2015 9:46 pm    Post subject: Reply with quote

Yes, mea culpa. My 'basics' must have included a dreaded 'correct mistake'
leading to an unearned conclusion.
Back to top
View user's profile Send private message
TerenceF



Joined: 21 Dec 2007
Posts: 26
Location: Takapuna, NZ

PostPosted: Sun Aug 16, 2015 11:46 am    Post subject: Reply with quote

Is this an allowable step?

Starting from Hugh's grid, if r3c5 is 4, then we have a chain of cells with 57 as the candidates, viz r1c4,r1c5,r7c5,r7c7,r9c7,r9c4,r1c4 (again) so the puzzle would have no unique solution.

So r3c5 <> 4, after which it reverts to singles.
Back to top
View user's profile Send private message
bat999



Joined: 09 Jul 2015
Posts: 55
Location: UK

PostPosted: Sun Aug 16, 2015 2:02 pm    Post subject: Reply with quote

TerenceF wrote:
Is this an allowable step?

... so the puzzle would have no unique solution....
Hi
There are a bunch of uniqueness tests.
Some of them are quite complicated. Confused
Here, for example --> http://sudopedia.enjoysudoku.com/Solving_Technique.html#Uniqueness
You need to show that your "allowable step" would cause it to fail a uniqueness test. Razz
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 568

PostPosted: Sun Aug 16, 2015 5:52 pm    Post subject: Reply with quote

TerenceF wrote:
Is this an allowable step?

Starting from Hugh's grid, if r3c5 is 4, then we have a chain of cells with 57 as the candidates, viz r1c4,r1c5,r7c5,r7c7,r9c7,r9c4,r1c4 (again) so the puzzle would have no unique solution.

So r3c5 <> 4, after which it reverts to singles.


Any of the experts out there like Marty or Keith could tell you at a glance! I remember hearing about 'deadly patterns' from them a while ago and your list of 57 cells looks to me like one of those well-known 6-cell deadly patterns - which would mean that the answer to your question is - yes, your solution is legit.
Back to top
View user's profile Send private message
Marty R.



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

PostPosted: Sun Aug 16, 2015 7:32 pm    Post subject: Reply with quote

Don's opinion notwithstanding, I am not an expert on anything. There have been a few people, George Woods' name comes to mind, who eschew uniqueness-based solutions. They never said why and I can't understand why they feel as they do, but the vast majority accepts those solutions.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Daily Sudoku 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