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 

Dec 20 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: 422
Location: Birmingham UK

PostPosted: Sun Dec 20, 2015 10:32 am    Post subject: Dec 20 VH Reply with quote

At last!
After basics:
Code:

+--------------+---------+-------------+
| 6    1   47  | 3  2 79 | 48  789 5   |
| 3    79  2   | 4  8 5  | 1   79  6   |
| 49   5   8   | 6  1 79 | 234 379 27  |
+--------------+---------+-------------+
| 148  48  9   | 5  7 3  | 6   2   18  |
| 158  6   15  | 9  4 2  | 38  378 178 |
| 7    2   3   | 8  6 1  | 5   4   9   |
+--------------+---------+-------------+
| 1489 489 14  | 12 3 6  | 7   5   28  |
| 158  78  157 | 12 9 4  | 28  6   3   |
| 2    3   6   | 7  5 8  | 9   1   4   |
+--------------+---------+-------------+

Play this puzzle online at the Daily Sudoku site

Looks like it needs two XY-wings to me:
Quote:
49-7 pivot r1c3 (or 47-9 pivot r1c3) followed by 79-4 pivot r2c2
Unless anyone knows different....

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



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

PostPosted: Sun Dec 20, 2015 4:11 pm    Post subject: Reply with quote

I agree.
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Sun Dec 20, 2015 5:00 pm    Post subject: Reply with quote

I had the same as Hugh too - but I'm also on a single-step chain-finding kick and this was the only one that I could find. I'm sure someone out there must have something better. (Oh, someone had better check this for accuracy too. I'm still sort of new at these.)

(7=9)r2c2-(9=4)r3c1-r4c1=r4c2-(49=8)r7c2-(8=2)r7c9-(2=7)r3c9-(7=9)r3c6-(9=7)r1c6 => r1c3<>7 which solves it (I think).
Back to top
View user's profile Send private message
Marty R.



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

PostPosted: Sun Dec 20, 2015 5:39 pm    Post subject: Reply with quote

dongrave wrote:
I had the same as Hugh too - but I'm also on a single-step chain-finding kick and this was the only one that I could find. I'm sure someone out there must have something better. (Oh, someone had better check this for accuracy too. I'm still sort of new at these.)

(7=9)r2c2-(9=4)r3c1-r4c1=r4c2-(49=8)r7c2-(8=2)r7c9-(2=7)r3c9-(7=9)r3c6-(9=7)r1c6 => r1c3<>7 which solves it (I think).


The chain looks legitimate to me. However, your deletion effectively does the same as the 47-9 XY-Wing, but that wasn't enough to solve.
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Sun Dec 20, 2015 6:05 pm    Post subject: Reply with quote

Marty R. wrote:

The chain looks legitimate to me. However, your deletion effectively does the same as the 47-9 XY-Wing, but that wasn't enough to solve.

No, that can't be right Marty. The XY wing gave us r13c6; my chain gives us r1c3=4 which solves it. (I always make sure that a chain solves the puzzle so I know it's a one-stepper.) Thanks!
Back to top
View user's profile Send private message
JC Van Hay



Joined: 13 Jun 2010
Posts: 494
Location: Charleroi, Belgium

PostPosted: Sun Dec 20, 2015 6:50 pm    Post subject: Reply with quote

dongrave wrote:
(7=9)r2c2-(9=4)r3c1-r4c1=r4c2-(49=8)r7c2-(8=2)r7c9-(2=7)r3c9-(7=9)r3c6-(9=7)r1c6 => r1c3<>7 which solves it (I think).
A shorter chain :
Code:
+-------------------+-------------+----------------+
| 6     1      (47) | 3   2  9(7) | 48   789  5    |
| 3     (79)   2    | 4   8  5    | 1    79   6    |
| 49    5      8    | 6   1  9(7) | 234  379  (27) |
+-------------------+-------------+----------------+
| 148   48     9    | 5   7  3    | 6    2    18   |
| 158   6      15   | 9   4  2    | 38   378  178  |
| 7     2      3    | 8   6  1    | 5    4    9    |
+-------------------+-------------+----------------+
| 1489  (489)  1-4  | 12  3  6    | 7    5    (28) |
| 158   78     157  | 12  9  4    | 28   6    3    |
| 2     3      6    | 7   5  8    | 9    1    4    |
+-------------------+-------------+----------------+
[XY-Wing(-479)L1C3,L27C2=8L7C2-(8=27)L73C9-7L3C3=7L1C6-(7=4)L1C3]-(4=1)L7C3
Back to top
View user's profile Send private message
Marty R.



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

PostPosted: Sun Dec 20, 2015 7:00 pm    Post subject: Reply with quote

Code:
+--------------+---------+-------------+
| 6    1   47  | 3  2 79 | 48  789 5   |
| 3    79  2   | 4  8 5  | 1   79  6   |
| 49   5   8   | 6  1 79 | 234 379 27  |
+--------------+---------+-------------+
| 148  48  9   | 5  7 3  | 6   2   18  |
| 158  6   15  | 9  4 2  | 38  378 178 |
| 7    2   3   | 8  6 1  | 5   4   9   |
+--------------+---------+-------------+
| 1489 489 14  | 12 3 6  | 7   5   28  |
| 158  78  157 | 12 9 4  | 28  6   3   |
| 2    3   6   | 7  5 8  | 9   1   4   |
+--------------+---------+-------------+


Don, you're gonna have to show me what I'm doing wrong.

Your chain => r1c3<>7=4
(7=4)r1c3-(4=9)r3c1-(9=7)r3c6. Here we are, doing the same thing as the 47-9 XY-Wing, removing 9 from r3c6, leaving a 7 there. That wasn't enough to solve and we had to go to a second wing.
Back to top
View user's profile Send private message
dongrave



Joined: 06 Mar 2014
Posts: 563

PostPosted: Sun Dec 20, 2015 8:17 pm    Post subject: Reply with quote

Marty R. wrote:

Don, you're gonna have to show me what I'm doing wrong.

Your chain => r1c3<>7=4
(7=4)r1c3-(4=9)r3c1-(9=7)r3c6. Here we are, doing the same thing as the 47-9 XY-Wing, removing 9 from r3c6, leaving a 7 there. That wasn't enough to solve and we had to go to a second wing.


Hi Marty, The difference is that the XY wing does not solve box 1 whereas the chain does - so the 4 in r1c3 gives us r1c7<>4=8 and r7c3<>4=1 and then they just branch out everywhere and solve the puzzle. It's an easy thing to overlook so I should have mentioned it in my previous post!
Back to top
View user's profile Send private message
Marty R.



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

PostPosted: Sun Dec 20, 2015 10:14 pm    Post subject: Reply with quote

OK, I had a similar situation here:

Code:
+----------+-------------+--------+
| 19 2  19 | 6    3   7  | 8  4 5 |
| 37 67 36 | 45   45  8  | 9  1 2 |
| 8  5  4  | 2    1   9  | 3  6 7 |
+----------+-------------+--------+
| 2  67 39 | 3479 479 1  | 46 5 8 |
| 39 4  5  | 8    69  36 | 2  7 1 |
| 17 8  16 | 47   2   5  | 46 3 9 |
+----------+-------------+--------+
| 5  9  2  | 37   67  36 | 1  8 4 |
| 6  1  8  | 59   59  4  | 7  2 3 |
| 4  3  7  | 1    8   2  | 5  9 6 |
+----------+-------------+--------+


I knew the correct solution in advance. My original answer had r4c5=4, which I knew to be correct. However when starting out solving that cell, it wouldn't complete. So I reworked my chains and was able to force r7c5=7, which goes all the way when solving that cell first.
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