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Daily Squiggly Sudoku: Tue 4-Apr-2006 Really very hard

 
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saharalaw
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PostPosted: Wed Apr 05, 2006 9:55 am    Post subject: Daily Squiggly Sudoku: Tue 4-Apr-2006 Really very hard Reply with quote

I can only solve most of the "9" , "2" and the first row "8" and "1".
Anyone can solve it in logic?
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mother superior
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PostPosted: Thu Apr 06, 2006 3:47 am    Post subject: april 4 squiggle Reply with quote

First of all, let me thank the webmaster for this puzzle. It is, without question, the most difficult of any puzzle ever posted on this site.
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Needless to say, I had a tough time with this one -- until I realized that the square at the bottom left hand corner could not be a seven. Until that realization, I spent an embarrassing amount of time staring blankly at the puzzle, making no progress at all.
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RogerC



Joined: 08 Oct 2005
Posts: 14
Location: High Wycombe, Bucks, England

PostPosted: Thu Apr 06, 2006 8:31 am    Post subject: Whyso? Reply with quote

Why, pray, Mother Superior, can the bottom left hand corner not be a seven?

I, too, am spending an embarrassing amount of time staring blankly at the puzzle. It has almost brought me to my knees, but perhaps not so much as you! Wink
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PGordon



Joined: 13 Apr 2006
Posts: 2
Location: New York City

PostPosted: Thu Apr 13, 2006 9:02 pm    Post subject: Daily Squiggly Tue 4-Apr-2006 Reply with quote

Very hard indeed. Part of my problem in understanding the discussion thread for this puzzle is that I'm unfamiliar with the numbering scheme. R and C for row and column are clear but are columns left to right or right to left, and rows top to bottom or bottom to top? Ditto "boxes": I'm accustomed to calling a cell a square and a 9-cell squiggly (or a straight 3x3 in a standard sudoku) a box. It may be that I'm on the wrong side of the Atlantic, but I could use clarification of everybody's notation.

Weren't there some posts from Steve on this puzzle? I can't seem to find them now that I've registered. RogerC's responses seemed on point, but I can't find them either. Is there something I don't know about how the forum works?

One other issue: I read in an academic paper on the subject (Cornell U. Math Department) that 23 "givens" are required to determine a single solution. It didn't discuss squigglies and, frankly, I didn't understand the rather off-hand proof, so it may not apply for squigglies. This puzzle is very short on givens. Anyone have any relevant info or comment?

This whole post sounds pretty feeble, but I really thought I'd gotten pretty good at this stuff (have happily solved all Standard "Very Hard" and all Squiggly "Hard" (and a couple of "Very Hard") that I've tried thus far (granted it's only been for the last couple of months).
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Thu Apr 13, 2006 9:14 pm    Post subject: Minimum Number Reply with quote

Quote:


I read in an academic paper on the subject (Cornell U. Math Department) that 23 "givens" are required to determine a single solution.



As far as is known, the minimum number of clues for a standard Sudoku with a single solution is 17. This is an observation, there is no proof.

As I recall, someone has made a collection of 17-clue puzzles. There are more than a few.

Keith
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Steve R



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

PostPosted: Thu Apr 13, 2006 10:43 pm    Post subject: Just to tidy up Reply with quote

Welcome PGordon.

The thread containing the discussion of the puzzle is nearby.

The columns are numbered 1 to 9 from left to right and the rows 1 to 9 from top to bottom. Boxes are numbered 1 to 9 as::
1 2 3
4 5 6
7 8 9

Gordon Royle’s collection of 36,628 essentially different classical Sudokus with 17 initial entries is published on his website.

Steve
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