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 

Chapeau!

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



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Sat Aug 04, 2007 2:57 pm    Post subject: Chapeau! Reply with quote

Congratulations to ravel on discovering the first minimal puzzle with 38 clues, which he published on 17 July:

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

It can be solved using the techniques commonly discussed in this forum though it is far from easy.

Donít despair if the second entry takes some time: after that is plain sailing.

Steve
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Aug 05, 2007 12:08 am    Post subject: Reply with quote

Nice puzzle.

I don't believe I found the "plain sailing" route. It took me 8 steps. All fairly well-known hereabouts... no chains, nothing uniqueness-based, no exotic coloring or the like.
Back to top
View user's profile Send private message Visit poster's website
Marty R.



Joined: 12 Feb 2006
Posts: 5179
Location: Rochester, NY, USA

PostPosted: Sun Aug 05, 2007 12:50 am    Post subject: Reply with quote

Quote:
...the first minimal puzzle with 38 clues...


Steve, what is a "minimal puzzle"?
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Aug 05, 2007 1:27 am    Post subject: Reply with quote

Marty's question sent me looking and I found these:

http://www.sudopedia.org/wiki/Minimal

http://www.sudopedia.org/wiki/Locally_minimal

http://www.sudopedia.org/wiki/Symmetrically_minimal

I have a question:

Is 38 the largest number of givens that has ever been found for a minimal puzzle, or are there minimal puzzles of, say, 39 or 40 givens but none of 38 had been found before?
Back to top
View user's profile Send private message Visit poster's website
Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Sun Aug 05, 2007 1:30 am    Post subject: Reply with quote

Asellus

Yes, it looks as though we might have gone different ways. I donít know how many steps I took but it was certainly eight or thereabouts. Iím glad you enjoyed it. So did I though I wouldnít want one like that every day.

Marty

A puzzle is minimal if it has a unique solution while the removal of any clue results in a puzzle with more than one solution. Evidently there is an upper limit to the number of clues which a minimal may have. It is far from certain that we shall ever find out what it is. To date work has concentrated on using computers to discover heavily clued puzzles.

I believe ravel suspects there will be a thirty-niner and is continuing the search.

Steve

PS (Added after Asellus's most recent post)

38 is the highest yet found. In the other direction 40,000 odd minimal puzzles with 17 clues are known.
Back to top
View user's profile Send private message
keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Sun Aug 05, 2007 9:33 pm    Post subject: I don't see it ... Reply with quote

After an X-wing and a W-wing:
Code:
+-------------------+-------------------+-------------------+
| 3     1     2     | 6     7     89    | 89    5     4     |
| 7     589   589   | 4     189   2     | 189   3     6     |
| 89    4     6     | 5     1389  1389  | 1789  179   2     |
+-------------------+-------------------+-------------------+
| 2459  7     1     | 3     459   49    | 2459  6     8     |
| 4589  6     59    | 2     14589 7     | 1459  19    3     |
| 2458  58    3     | 19    6     148   | 12457 127   79    |
+-------------------+-------------------+-------------------+
| 568   35    58    | 19    2     136   | 367   4     79    |
| 1     39    7     | 8     349   3469  | 2369  29    5     |
| 69    2     4     | 7     39    5     | 369   8     1     |
+-------------------+-------------------+-------------------+
Now, what?

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



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sun Aug 05, 2007 9:48 pm    Post subject: Reply with quote

Keith,

Look at R1349 and think big!
Back to top
View user's profile Send private message Visit poster's website
keith



Joined: 19 Sep 2005
Posts: 3184
Location: near Detroit, Michigan, USA

PostPosted: Sun Aug 05, 2007 11:44 pm    Post subject: Reply with quote

I still don't see it.

If it is a chain, I don't buy it.

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



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Mon Aug 06, 2007 1:52 am    Post subject: Reply with quote

I didn't spot Asellus's fish. My next six steps were:

1 Eliminate 8 from r2c5 using the conjugates (r5c1, r5c5) and (r2c2, r6c2) with respect to 8.
2 Eliminate 9 from r3c7 and r3c8 using the w-wing pivoted on the conjugates (r1c6, {r3c5, r3c6}) with respect to 8 and the pincers (89) in r1c7 and r3c1
3 Eliminate 7 from r6c8 using the xy-wing for (19) pivoted on r5c8 with pincers r3c8 and r6c9
4 The only place for 7 in column 8 is r3c8
5 Eliminate 1 from r5c5 using the w-wing pivoted on the conjugates (r2c3, r5c3) with respect to 9 and the pincers (19) in r2c5 and r5c8
6 The only place for 1 in row 5 is r5c8

Singles follow. (At least I hope they do: I didn't quite have Keith's position. It was very close and I have bodged to fill the gap.)

Steve
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Mon Aug 06, 2007 2:29 am    Post subject: Reply with quote

As Steve noted, I was hinting at the Finned Jellyfish on 9. It eliminates <9> from R2C7.

Next, I too eliminated <8> from R2C5, though I saw it as a Box 1 ER using the R5 pair rather than as Steve's "Kite" or "Color Wrap". (So many ways to see the same thing.)

After that...

XY Wing: Pivot R2C7 eliminates <9> from R1C6. 8, 5 and 4 are now determined in C5, <1>s simplify a bit, etc.

Color Wrap or Kite out of Box 7 eliminates <9> from R2C5.

Then, an XY Wing: Pivot R6C8 eliminates <9> from R7C9, finishing things off.
Back to top
View user's profile Send private message Visit poster's website
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