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 

many ways to crack this egg

 
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 Nov 29, 2007 3:42 pm    Post subject: many ways to crack this egg Reply with quote

In today's Vanheugen "fiendish" http://www.playr.co.uk/sudoku/index.php?class=5
Code:
+-----------+-----------+-----------+
|  .  9  .  |  1  .  2  |  .  .  .  |
|  .  2  .  |  .  4  6  |  9  3  1  |
|  .  4  .  |  .  5  .  |  .  .  .  |
+-----------+-----------+-----------+
|  9  6  .  |  .  2  .  |  .  .  7  |
|  .  5  2  |  3  .  7  |  8  9  .  |
|  7  .  .  |  .  9  .  |  .  4  3  |
+-----------+-----------+-----------+
|  .  .  .  |  .  7  .  |  .  6  .  |
|  2  7  9  |  5  6  .  |  .  8  .  |
|  .  .  .  |  2  .  4  |  .  1  .  |
+-----------+-----------+-----------+

it is almost embarrassing how quickly one gets to the point:

Code:


+--------------------------+--------------------------+--------------------------+
| 368     9       68       | 1       38      2        | 4       7       5        |
| 58      2       578      | 78      4       6        | 9       3       1        |
| 13      4       17       | 79      5       39       | 6       2       8        |
+--------------------------+--------------------------+--------------------------+
| 9       6       3        | 4       2       8        | 1       5       7        |
| 4       5       2        | 3       1       7        | 8       9       6        |
| 7       18      18       | 6       9       5        | 2       4       3        |
+--------------------------+--------------------------+--------------------------+
| 18      138     4        | 89      7       39       | 5       6       2        |
| 2       7       9        | 5       6       1        | 3       8       4        |
| 56      38      56       | 2       38      4        | 7       1       9        |
+--------------------------+--------------------------+--------------------------+


Plenty of ways to go from here:
a) coloring:
to remove 8 from r2c3 use this chain: -r2c4=r1c5-r9c5=r9c2-r6c2=r6c3-
(but still needs xy wing later on)

b) xy-wings:
pivot r1c3 removes 5 from the same cell r2c3 and from r9c1
pivot r2c1 removes 6 from r9c3 and r1c1

c) w-wings:
r6c2/r7c1 (by way of r6c3,r3c3,r3c4,r7c4)
r1c5/r9c2 (r2c4,r3c4,r3c6,r3c1,r7c1)

more?
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: Thu Nov 29, 2007 4:40 pm    Post subject: Reply with quote

how about xy-chain:

r7c6=9, r7c4=8, r7c1=1, r3c1=3, r3c6<>3
Back to top
View user's profile Send private message
nataraj



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

PostPosted: Thu Nov 29, 2007 5:14 pm    Post subject: Reply with quote

storm_norm wrote:
how about xy-chain:


True. I know, I know. Tons of xy-chains. Yuck.

No, I take it back. Sorry for the language. Just spent half an hour wading in chains.

They're great.
Back to top
View user's profile Send private message Send e-mail Visit poster's website
nataraj



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

PostPosted: Thu Nov 29, 2007 5:18 pm    Post subject: Reply with quote

Isn't that a BUG+3 situation, too?

r1c1=8 OR r2c3=8 OR r7c2=8 ?

either way, r2c1<>8, the resulting BUG+1 solves it with r7c2=8 .


Last edited by nataraj on Thu Nov 29, 2007 5:28 pm; edited 1 time in total
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: Thu Nov 29, 2007 5:28 pm    Post subject: Reply with quote

well I saw, 3,9 in column 6, and some other 3's and 9's so I went with it. yuck is right.
Back to top
View user's profile Send private message
keith



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

PostPosted: Thu Nov 29, 2007 6:08 pm    Post subject: Reply with quote

nataraj wrote:
Isn't that a BUG+3 situation, too?

r1c1=8 OR r2c3=8 OR r7c2=8 ?

either way, r2c1<>8, the resulting BUG+1 solves it with r7c2=8 .


As I see it, the BUG+3 means R1C3 <>8, which leads to a remote naked pair <38> which solves the puzzle.

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



Joined: 28 Oct 2007
Posts: 80

PostPosted: Thu Nov 29, 2007 8:30 pm    Post subject: Re: many ways to crack this egg Reply with quote

nataraj wrote:

Plenty of ways to go from here:
a) coloring:
to remove 8 from r2c3 use this chain: -r2c4=r1c5-r9c5=r9c2-r6c2=r6c3-
(but still needs xy wing later on)

Start 3D-multicoloring from say r1c5. You will only need two colors and you quickly find a wealth of deductions.
Back to top
View user's profile Send private message
ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Thu Nov 29, 2007 10:14 pm    Post subject: Reply with quote

Code:
+--------------------------+--------------------------+--------------------------+
|#368     9      #68       | 1       38      2        | 4       7       5        |
|#58      2      #578      | 78      4       6        | 9       3       1        |
| 13      4       17       | 79      5       39       | 6       2       8        |
+--------------------------+--------------------------+--------------------------+
| 9       6       3        | 4       2       8        | 1       5       7        |
| 4       5       2        | 3       1       7        | 8       9       6        |
| 7       18      18       | 6       9       5        | 2       4       3        |
+--------------------------+--------------------------+--------------------------+
| 18      138     4        | 89      7       39       | 5       6       2        |
| 2       7       9        | 5       6       1        | 3       8       4        |
|#56      38     #56       | 2       38      4        | 7       1       9        |
+--------------------------+--------------------------+--------------------------+
Alternatively to the BUG+3 you can use this deadly pattern (68,58,56). Because of the strong links for 6 in row 1 and 5 in r2 it eliminates 8 from r1c3 and r2c1, 6 from r1c1 and r9c3, and 5 from r2c3 and r9c1.
The BUG+1 finishes it then.
Back to top
View user's profile Send private message
re'born



Joined: 28 Oct 2007
Posts: 80

PostPosted: Fri Nov 30, 2007 9:23 am    Post subject: Reply with quote

ravel wrote:
Code:
+--------------------------+--------------------------+--------------------------+
|#368     9      #68       | 1       38      2        | 4       7       5        |
|#58      2      #578      | 78      4       6        | 9       3       1        |
| 13      4       17       | 79      5       39       | 6       2       8        |
+--------------------------+--------------------------+--------------------------+
| 9       6       3        | 4       2       8        | 1       5       7        |
| 4       5       2        | 3       1       7        | 8       9       6        |
| 7       18      18       | 6       9       5        | 2       4       3        |
+--------------------------+--------------------------+--------------------------+
| 18      138     4        | 89      7       39       | 5       6       2        |
| 2       7       9        | 5       6       1        | 3       8       4        |
|#56      38     #56       | 2       38      4        | 7       1       9        |
+--------------------------+--------------------------+--------------------------+
Alternatively to the BUG+3 you can use this deadly pattern (68,58,56). Because of the strong links for 6 in row 1 and 5 in r2 it eliminates 8 from r1c3 and r2c1, 6 from r1c1 and r9c3, and 5 from r2c3 and r9c1.
The BUG+1 finishes it then.

I'm not satisfied with the deadly pattern. The rule of thumb ronk taught me for deciding whether something is a deadly pattern is that each candidate in the pattern should occur twice in every row, column and block. In this case 8 occurs 4 times in the pattern in block 1 and so I would think it would not be a deadly pattern. Thoughts?
Back to top
View user's profile Send private message
keith



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

PostPosted: Fri Nov 30, 2007 11:36 am    Post subject: Reply with quote

re'born wrote:
ravel wrote:
Code:
+--------------------------+--------------------------+--------------------------+
|#368     9      #68       | 1       38      2        | 4       7       5        |
|#58      2      #578      | 78      4       6        | 9       3       1        |
| 13      4       17       | 79      5       39       | 6       2       8        |
+--------------------------+--------------------------+--------------------------+
| 9       6       3        | 4       2       8        | 1       5       7        |
| 4       5       2        | 3       1       7        | 8       9       6        |
| 7       18      18       | 6       9       5        | 2       4       3        |
+--------------------------+--------------------------+--------------------------+
| 18      138     4        | 89      7       39       | 5       6       2        |
| 2       7       9        | 5       6       1        | 3       8       4        |
|#56      38     #56       | 2       38      4        | 7       1       9        |
+--------------------------+--------------------------+--------------------------+
Alternatively to the BUG+3 you can use this deadly pattern (68,58,56). Because of the strong links for 6 in row 1 and 5 in r2 it eliminates 8 from r1c3 and r2c1, 6 from r1c1 and r9c3, and 5 from r2c3 and r9c1.
The BUG+1 finishes it then.

I'm not satisfied with the deadly pattern. The rule of thumb ronk taught me for deciding whether something is a deadly pattern is that each candidate in the pattern should occur twice in every row, column and block. In this case 8 occurs 4 times in the pattern in block 1 and so I would think it would not be a deadly pattern. Thoughts?


Well, the pattern that ravel is avoiding is this:
Code:
+------------+
| 68  .  68  |
| 58  .  58  |
| .   .  .   |
+------------+
| .   .  .   |
| .   .  .   |
| .   .  .   | 
+------------+
| .   .  .   |
| .   .  .   |
| 56  .  56  |
+------------+

which is clearly not a valid pattern. But, I think ravel's logic is correct. He is avoiding an invalid solution (pattern), albeit not one that has multiple solutions The more usual deadly pattern would be like this:
Code:
+------------+
| 68  .  68  |
| .   .  .   |
| .   .  .   |
+------------+
| .   .  .   |
| 58  .  58  |
| .   .  .   | 
+------------+
| .   .  .   |
| .   .  .   |
| 56  .  56  |
+------------+


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



Joined: 21 Apr 2006
Posts: 536

PostPosted: Fri Nov 30, 2007 11:41 am    Post subject: Reply with quote

re'born wrote:
I'm not satisfied with the deadly pattern. The rule of thumb ronk taught me for deciding whether something is a deadly pattern is that each candidate in the pattern should occur twice in every row, column and block. In this case 8 occurs 4 times in the pattern in block 1 and so I would think it would not be a deadly pattern. Thoughts?
Ah, thanks, of course you are right. This pattern in one box definitely is impossible.
Code:
+--------------------------+
| 68      .       68       |
| 58      .       58       |
-----

I deleted the other post, where i made the same mistake, but the eliminations were not correct.

PS:
This is a deadly pattern with 3 digits in a box:
Code:
| abc abc abc |
|  .   .   .  |
|  .   .   .  |
--------------
| abc abc abc |
|  .   .   .  |
|  .   .   .  |
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