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 

DB Saturday Puzzle - July 8, 2006

 
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: 3174
Location: near Detroit, Michigan, USA

PostPosted: Sat Jul 08, 2006 11:38 am    Post subject: DB Saturday Puzzle - July 8, 2006 Reply with quote

Here is today's puzzle:
Code:
Puzzle: DB070806  ******
+-------+-------+-------+
| . . . | . . 5 | 3 1 . |
| . 7 . | 2 . . | . 6 . |
| . . . | 9 . . | . . 4 |
+-------+-------+-------+
| . . 7 | . 4 . | . 3 6 |
| . 4 9 | . . . | 1 2 . |
| 1 2 . | . 5 . | 7 . . |
+-------+-------+-------+
| 7 . . | . . 1 | . . . |
| . 9 . | . . 7 | . 5 . |
| . 3 8 | 5 . . | . . . |
+-------+-------+-------+

I'll post my comments later.

Keith


Last edited by keith on Sun Jul 09, 2006 12:52 pm; edited 2 times in total
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5162
Location: Rochester, NY, USA

PostPosted: Sat Jul 08, 2006 5:10 pm    Post subject: Reply with quote

This one was solved pretty quickly. All basic stuff, with a Type 4 thrown in.
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3174
Location: near Detroit, Michigan, USA

PostPosted: Sun Jul 09, 2006 12:51 pm    Post subject: An interesting UR Reply with quote

I thought this one was interesting.

First, if you ignore the Unique Rectangle, it can be solved with an XY-wing.

Second, you can exploit the UR in a number of ways, if you do not do all the other basic eliminations first. I first found the UR at this point:
Code:

+----------------+----------------+----------------+
| 9    68   246  | 468  68   5    | 3    1    7    |
| 348  7    34   | 2    1    348  | 5    6    9    |
| 356  1    356  | 9    367  36   | 2    8    4    |
+----------------+----------------+----------------+
| 58   58   7    | 1    4    2    | 9    3    6    |
| 368  4    9    | 3678 3678 368  | 1    2    5    |
| 1    2    36   | 36   5    9    | 7    4    8    |
+----------------+----------------+----------------+
| 7    56   2456 | 3468 2368 1    | 468  9    23   |
| 246  9    1    | 3468 2368 7    | 468  5    23   |
| 246  3    8    | 5    269  46   | 46   7    1    |
+----------------+----------------+----------------+

The UR on <23> is a Type 3 in R78C59. Note that the extra values <68> form a reduced set with <68> in R1C5, so you can eliminate <68> from R359C5.

After a couple more hidden singles, we get
Code:
+----------------+----------------+----------------+
| 9    68   2    | 4    68   5    | 3    1    7    |
| 348  7    34   | 2    1    38   | 5    6    9    |
| 356  1    356  | 9    37   36   | 2    8    4    |
+----------------+----------------+----------------+
| 58   58   7    | 1    4    2    | 9    3    6    |
| 368  4    9    | 3678 37   368  | 1    2    5    |
| 1    2    36   | 36   5    9    | 7    4    8    |
+----------------+----------------+----------------+
| 7    56   456  | 368  2368 1    | 468  9    23   |
| 246  9    1    | 368  2368 7    | 468  5    23   |
| 246  3    8    | 5    29   46   | 46   7    1    |
+----------------+----------------+----------------+

The UR is still a Type 3, the reduced set is with <368> in box 8, and the reduction is R9C6 is not <6>, it must be <4>.

Then, having solved R9, the UR is a Type 4, and we can eliminate <3> from R78C5.

(The XY-wing turns up in R5C6, and eliminates <3> in R2C1. It is not in the above diagrams.)

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



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Sun Jul 09, 2006 2:28 pm    Post subject: Not quite as tricky Reply with quote

Hi, Keith!

I worked this one in the newspaper before I saw your post. I managed to get through it without any pencil marks, but I did rely on the "UR" in r78c59 to do it. My analysis wasn't nearly as sophisticated as yours, though.

After doing the basic stuff I arrived here.
Code:
+---------------+-----------------+---------------+
|   9   68  2   |  468   68   5   |   3   1   7   |
|  348  7   34  |   2    1   348  |   5   6   9   |
|  356  1  356  |   9    7    36  |   2   8   4   |
+---------------+-----------------+---------------+
|   58  58  7   |   1    4    2   |   9   3   6   |
|   36  4   9   |   7   368  368  |   1   2   5   |
|   1   2   36  |   36   5    9   |   7   4   8   |
+---------------+-----------------+---------------+
|   7   56 456  |  3468 2368  1   |  468  9   23  |
|   46  9   1   |  3468 2368  7   |  468  5   23  |
|   2   3   8   |   5    9    46  |   46  7   1   |
+---------------+-----------------+---------------+

I reasoned as follows -- since the "2" in box 8 must appear in column 5, there can't be a "3" at either r7c5 or r7c8. Therefore r5c5 = 3, and the rest of it fell out pretty easily. dcb
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Marty R.



Joined: 12 Feb 2006
Posts: 5162
Location: Rochester, NY, USA

PostPosted: Sun Jul 09, 2006 4:18 pm    Post subject: Reply with quote

Quote:
First, if you ignore the Unique Rectangle, it can be solved with an XY-wing.


I don't have the will power to ignore it. Smile Generally, I follow the path of least resistance to the solution and you guys are theoreticians who enjoy dissecting the puzzles to see how many different techniques can be used to solve them. That's not a criticism, as these puzzles are here for us to do anything with them that gives us enjoyment.

Do you do your puzzles via computer and do a "save" at various stages? Otherwise, how are you able to post these intermediate positions? As a pencil-and-paper guy, the only way I could do it is if I typed the grid into Notepad, anticipating a need to later use it. Question
Back to top
View user's profile Send private message
TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Sun Jul 09, 2006 6:45 pm    Post subject: Reply with quote

The program I use (and I'm assuming others are similar) has an 'undo' buttom, which I can use to show the pencilmarks at any particular spot in my solving process. It's especially nice if I want to disect the puzzle (which I usually don't since I'm in the least resistance solving club also), because, once it is solved (if I get that far) I can go back to the beginning, see what cell was solved or number was excluded at each subsequent step, without having to remember how I did it, while looking for alternative methods if I so desire.
Back to top
View user's profile Send private message
David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Sun Jul 09, 2006 9:10 pm    Post subject: Paper vs computers Reply with quote

Marty R wrote:
Do you do your puzzles via computer and do a "save" at various stages?

On this particular puzzle I worked the whole thing out with pencil and paper. I felt particularly good about it, because I was able to "see" the whole thing through without making any auxiliary pencil marks.

Later, when I saw Keith's analysis of the "UR" pattern I had recognized, I went back and used a computer program to reconstruct the position I got to, or something reasonably close to it. That was fairly easy to do, since the program I generally use ("Simple Sudoku") has a paper and pencil emulation mode, where all one sees are the completed numbers. So it was just like working the puzzle over again, and I'm sure I came pretty close to doing it the same way the second time through. dcb
Back to top
View user's profile Send private message Send e-mail Visit poster's website
keith



Joined: 19 Sep 2005
Posts: 3174
Location: near Detroit, Michigan, USA

PostPosted: Mon Jul 10, 2006 10:39 pm    Post subject: Sudoku Software Reply with quote

Marty (and others),

I solve puzzles with pencil and paper.

But, before I post an analysis of a puzzle, I use Sudoku Susser to check my logic and to generate the puzzle grids to post as "code". Susser has a log from which you can cut and paste; It also has an option to log the current puzzle at every move.

Susser also has the capability to save the state of a puzzle, but it is a little cumbersome (each state is a different file). Mostly, I just keep the initial puzzle. When solving, you have the option to go back one step (and one more step, etc.), or to reset the puzzle to its initial position.

What I am trying to say is, yes, you can go back, but it does not implement "backtracking" as a solution technique.

I also use Susser to help solve puzzles when I get stuck. What I usually find is that there is some bookkeeping error in my pencilmarks. Or, stupid me, I did not see that 11-link chain!

I can't speak for other software, but an application like Susser is an excellent learning tool. Not to solve puzzles with, but to re-examine how you solved (or not) a particular puzzle.

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



Joined: 12 Feb 2006
Posts: 5162
Location: Rochester, NY, USA

PostPosted: Tue Jul 11, 2006 3:57 pm    Post subject: Reply with quote

Keith,

I had downloaded the Susser some months ago, at your recommendation and with some assistance. But it was for reading about techniques, not using as a tool.

At any rate, I haven't looked at it lately, but I recall it's about a 95-page document and I've looked through it a couple of times and coudn't see anything that looked like a computer solver, or whatever it's called. But then, I'm no computer genius either.
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3174
Location: near Detroit, Michigan, USA

PostPosted: Tue Jul 11, 2006 7:18 pm    Post subject: Sudoku Susser Reply with quote

Marty,

When you download Sudoku Susser, you get a zip file. When you unzip it, you will find the manual (the PDF document you describe) and also an executable, sudoku.exe. This is the computer program.

Just unzip the files, and put them in some directory. Double-click on sudoku.exe, and the software will run. If you need further help, we can do it by mail.

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



Joined: 12 Feb 2006
Posts: 5162
Location: Rochester, NY, USA

PostPosted: Wed Jul 12, 2006 5:12 pm    Post subject: Reply with quote

OK, I did all that and found the program. If I have the time and inclination to get through the voluminous instructions, it'll be awhile.

Thank you.

P.S. I wonder what a "susser" is. Other than something that susses. Laughing
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3174
Location: near Detroit, Michigan, USA

PostPosted: Wed Jul 12, 2006 6:39 pm    Post subject: Reply with quote

1. sussed
Generally used as friendly replacement of "figured out", "worked out" or "done".

"You've got it all sussed out don't you, Mac?"


2. sussed

Discovered the answer. Achieved individual enlightenment regarding a current problem or dilema.

Ah, I think I've sussed it...
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5162
Location: Rochester, NY, USA

PostPosted: Thu Jul 13, 2006 3:59 pm    Post subject: Reply with quote

Two dozen lashes with a wet noodle for me for not checking a dictionary first, which is odd, since I'm a frequent dictionary user. Mad

Friday, while out on the lake, if we're fortunate enough to locate some bass, I'll impress my partner and say, "yeah Jeff, I think we've got these bass sussed out." Laughing
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