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 

May 15 NVH?

 
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: 422
Location: Birmingham UK

PostPosted: Sun May 15, 2016 9:42 am    Post subject: May 15 NVH? Reply with quote

After basics (but not all):
Code:

+----------------+-------------+------------+
| 6   57    578  | 18  4   23  | 15 23  9   |
| 123 9     138  | 5   368 236 | 7  236 4   |
| 235 4     35   | 136 9   7   | 15 236 8   |
+----------------+-------------+------------+
| 137 1367  9    | 2   5   36  | 8  4   16  |
| 145 156   2    | 468 68  9   | 3  7   156 |
| 345 8     356  | 346 7   1   | 2  9   56  |
+----------------+-------------+------------+
| 8   23567 3567 | 9   236 45  | 46 1   37  |
| 137 12367 4    | 367 236 8   | 9  5   37  |
| 9   3567  3567 | 367 1   45  | 46 8   2   |
+----------------+-------------+------------+



Play this puzzle online at the Daily Sudoku site

A Check on the grade of the above diagram gets "Very Hard' despite
the obvious single 1 in C3. After entering the 1 the grade changes to Easy.
I suspect the bug in the algorithm is around perceiving certain Box-line
reductions as X-Wings (some are very similar). Any other ideas?

Hugh
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Sun May 15, 2016 3:58 pm    Post subject: Reply with quote

This one's even more surprising than the others! Hey! Wait a minute! No, it's not that surprising. I don't think it quite reached your grid. I think you're right about your Box/Line Reduction theory. I think it's not always correctly prioritizing the locked candidates (in this case, the locked 1's in row 2 of box 1) and is instead applying a Wing on the grid that you posted but with a 1 still in r1c23 and r3c13 (because I don't think it made the last move that you made to eliminate them). I think you're right. I think it's hit or miss when it comes down to a Box/Line Reduction or a Wing.

Update: By the way, I forgot to mention - in this case, the X Wing that it probably applied was the 1's in columns 4 and 7 which removes the exact same candidates as the locked 1's in row 2!
Back to top
View user's profile Send private message
hughwill



Joined: 05 Apr 2010
Posts: 422
Location: Birmingham UK

PostPosted: Mon May 16, 2016 11:10 am    Post subject: Reply with quote

I've always assumed that where there's a box-line reduction any X wing that
does the same job is not really an X-wing because basics take precedence.
However this distinction is arbitrary. On much rarer occasions I've noticed that
puzzles which can be done with basics include XY or XYZ wings though I don't
think the algorithm is ever fooled by these in the same way.
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Mon May 16, 2016 12:11 pm    Post subject: Reply with quote

Oh, I think you're definitely right! I should have said 'when it comes down to a Box/Line Reduction or an X-Wing' (not 'or a Wing'). Thanks Hugh!
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