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 

I learned something new ...

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



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

PostPosted: Fri Apr 30, 2021 6:35 pm    Post subject: I learned something new ... Reply with quote

Code:
+-------+-------+-------+
| 5 . . | . . 8 | . 4 3 |
| . . . | 5 9 4 | . . . |
| 7 1 . | 3 . . | . . . |
+-------+-------+-------+
| . 7 5 | . 4 . | . . 8 |
| . . 6 | . . . | 1 . . |
| 9 . . | . 8 . | 5 2 . |
+-------+-------+-------+
| . . . | . . 3 | . 8 5 |
| . . . | 4 1 7 | . . . |
| 3 6 . | 8 . . | . . 2 |
+-------+-------+-------+

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



Joined: 06 Mar 2014
Posts: 443

PostPosted: Sat May 01, 2021 12:56 pm    Post subject: Reply with quote

After basics:

Code:
+------------+----------+--------+
| 5   29  29 | 1  7  8  | 6 4 3  |
| 6   38  38 | 5  9  4  | 2 7 1  |
| 7   1   4  | 3  26 26 | 8 5 9  |
+------------+----------+--------+
| 12  7   5  | 9  4  12 | 3 6 8  |
| 248 248 6  | 27 3  5  | 1 9 47 |
| 9   34  13 | 67 8  16 | 5 2 47 |
+------------+----------+--------+
| 14  49  19 | 26 26 3  | 7 8 5  |
| 28  5   28 | 4  1  7  | 9 3 6  |
| 3   6   7  | 8  5  9  | 4 1 2  |
+------------+----------+--------+

Then I used the following chain:

(1=2)r4c1 - r8c1 = r8c3 - (2=9)r1c3 - (9=1)r7c3 => r6c3 <> 1; stte.

What did you use to solve it Keith?
Back to top
View user's profile Send private message
keith



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

PostPosted: Sat May 01, 2021 6:34 pm    Post subject: Reply with quote

After basics (see dongrave's grid above), this puzzle is a BUG+2.

In a BUG, every unsolved cell has two candidates, and each candidate occurs twice in each house (row, column, or box). A BUG does not have a unique solution: It has zero or two solutions (I believe).

Code:
+-----------------+-------------+-------------+
|  5     29   29  | 1   7   8   | 6   4   3   |
|  6     38   38  | 5   9   4   | 2   7   1   |
|  7     1    4   | 3   26  26  | 8   5   9   |
+-----------------+-------------+-------------+
|  12    7    5   | 9   4   12  | 3   6   8   |
| (2)48 2(4)8 6   | 27  3   5   | 1   9   47  |
|  9     34   13  | 67  8   16  | 5   2   47  |
+-----------------+-------------+-------------+
|  14    49   19  | 26  26  3   | 7   8   5   |
|  28    5    28  | 4   1   7   | 9   3   6   |
|  3     6    7   | 8   5   9   | 4   1   2   |
+-----------------+-------------+-------------+

The "+2" candidates are 2 in R5C1 and 4 in R5C1. You can see this by checking the candidates in C1 and then in C2, and noting then that the BUG condition is satisfied also in R5 and B4 if 2 is eliminated in R5C1 and 4 in R5C2.

Now, the correct statement, in this case, for a single unique solution is: R5C1 is 2 AND/OR R5C2 is 4.

(Here I was wrong. I thought the condition is always AND. In nearly 20 years of solving these things, I have never seen a case where the correct choice is OR.)

In either case, R5C1 is not 4 or R5C2 is not 2, and either of these eliminations solves the puzzle. We find R5C1=2 and R5C2=8.

Keith

(Thanks to Leren and Jamil for correcting me in another forum.)
Back to top
View user's profile Send private message
ZeroAssoluto



Joined: 05 Feb 2017
Posts: 632
Location: Rimini, Italy

PostPosted: Sun May 02, 2021 12:42 pm    Post subject: Reply with quote

Hi everyone,

WXYZ-Wing 1,2,3,8 in r268c3,r4c1 and -2 in r8c1

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



Joined: 06 May 2017
Posts: 455

PostPosted: Mon May 03, 2021 3:10 pm    Post subject: Reply with quote

Thanks Keith. Great clarification of the rare BUG+2 phenomenon. I had not been able to do much with them until now.

cheers...immp
Back to top
View user's profile Send private message
immpy



Joined: 06 May 2017
Posts: 455

PostPosted: Mon May 03, 2021 3:16 pm    Post subject: Reply with quote

Question: Will this only work when the BUG cells see each other, or can it be applied in any case?

Thanks in advance for any enlightenment.
Back to top
View user's profile Send private message
keith



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

PostPosted: Mon May 03, 2021 7:52 pm    Post subject: Reply with quote

immpy wrote:
Question: Will this only work when the BUG cells see each other, or can it be applied in any case?

Thanks in advance for any enlightenment.

immpy,

The process is to identify the candidates which if eliminated will leave a BUG. That is, every unsolved cell is a bivalue, and each unsolved digit occurs twice in each row, column, and box. Then, one (or more) of those candidates must be true.

How that plays out I think depends on the particular puzzle. I'll try to find more examples.

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



Joined: 06 May 2017
Posts: 455

PostPosted: Tue May 04, 2021 2:51 pm    Post subject: Reply with quote

I got it Keith. And it would depend on the particular puzzle. Thanks.

cheers...immp
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