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DB Saturday puzzle (March 11)

 
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keith



Joined: 19 Sep 2005
Posts: 3150
Location: near Detroit, Michigan, USA

PostPosted: Sat Mar 11, 2006 9:15 am    Post subject: DB Saturday puzzle (March 11) Reply with quote

Here is today's David Bodycombe puzzle. I had fun with it.

Keith

Code:


Puzzle: DB031106 ******
+-------+-------+-------+
| . 7 . | . . . | 1 . 3 |
| . . . | 8 1 . | . 5 . |
| 9 1 . | 5 . . | 6 . . |
+-------+-------+-------+
| . . . | . 5 . | . . 4 |
| . 4 5 | . . . | 8 9 . |
| 6 . . | . 2 . | . . . |
+-------+-------+-------+
| . . 2 | . . 1 | . 3 5 |
| . 5 . | . 6 9 | . . . |
| 8 . 9 | . . . | . 1 . |
+-------+-------+-------+

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Steve R



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

PostPosted: Sat Mar 11, 2006 5:36 pm    Post subject: Very hard becomes a nightmare Reply with quote

Thanks for DB’s latest, Keith. Like you I enjoyed it considerably, though it was tough going by my standards.

In fact it was the second hard slog of the week, the first being samgj’s very hard of 9 March. You might like to try it after moving the 7 in row 1 one cell to the left. This is the result:
Code:
-------------------------
| . . 6 | 9 7 . | . . 4 |
| . . . | . . . | 6 7 . |
| 7 . . | . . . | 1 . 5 |
-------------------------
| . . . | . 5 9 | . . 1 |
| 3 5 . | . . . | . 2 6 |
| 8 . . | 6 4 . | . . . |
-------------------------
| 9 . 4 | . . . | . . 8 |
| . 8 5 | . . . | . . . |
| 6 . . | 8 . 5 | 9 . . |
-------------------------

DB would be horrified at the asymmetry but not, I think, too ashamed of the challenge which resulted.

Steve
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David Bryant



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

PostPosted: Sat Mar 11, 2006 6:28 pm    Post subject: It's a good puzzle Reply with quote

I liked the Bodycombe puzzle too -- coloring on the "7"s plus one XY-Wing did the trick for me.

Steve, I'm curious how you found the permutation on samgj's puzzle. Do you often look for slight alterations like that? How often does a valid puzzle result? dcb
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Steve R



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

PostPosted: Sat Mar 11, 2006 9:22 pm    Post subject: It's a good puzzle Reply with quote

No. I put it in a solver to check that it involved more than singles, made a transcription error and became interested.

I have tinkered with puzzles on only three occasions, using a solver to see if the symmetric original could be reconstructed from partially worked grids found on web sites. I succeeded the first time but on each occasion stumbled through too many multiple solution or invalid grids to recommend the practice.

Steve
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Marty R.



Joined: 12 Feb 2006
Posts: 5124
Location: Rochester, NY, USA

PostPosted: Sat Mar 11, 2006 11:48 pm    Post subject: Reply with quote

Keith, I also like that you post these DB puzzles. This one I was able to solve with the use of two forcing chains.
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keith



Joined: 19 Sep 2005
Posts: 3150
Location: near Detroit, Michigan, USA

PostPosted: Sun Mar 12, 2006 12:46 am    Post subject: Reasons to post puzzles Reply with quote

Marty, Steve, David, and all:

I have been posting these puzzles only when they involve something more than "basic" techniques.

I think of basic techniques as forced and pinned values, naked and hidden sets, and row / block / column interactions. I have not yet seen a Daily Sudoku that requires more than these techniques.

The next (intermediate?) level includes X and XY-wings, swordfish, unique rectangles, BUG patterns, simple coloring, and the like. The DB puzzles I have posted involve these.

I think of the various chain techniques as "advanced", possibly because I have such difficulty seeing them.

Anyway, I am not trying to start a debate on classification of solution strategies. This is a long way of explaining why I posted three puzzles two weeks ago, none last week, and only one this week.

Keith


Last edited by keith on Sun Mar 12, 2006 2:49 am; edited 1 time in total
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David Bryant



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

PostPosted: Sun Mar 12, 2006 1:53 am    Post subject: The modified 3/09/06 puzzle Reply with quote

Steve R wrote:
... it was the second hard slog of the week, the first being samgj’s very hard of 9 March. You might like to try it after moving the 7 in row 1 one cell to the left.

Thanks for the "extra" puzzle, Steve.

I used coloring on the "2"s plus a double-implication chain to get through this one. I also noticed that one could get there by finding a swordfish pattern, plus an XY-Wing.

An extremely interesting variation on one of samgj's better puzzles! Thanks again. dcb
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someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich

PostPosted: Sun Mar 12, 2006 3:58 pm    Post subject: Reply with quote

Hi,
could not resist to take a look at this one.
I found a nice 5 star in the following places:
r2c6 = 47
r2c7 = 47
r3c5 = 347
r9c5 = 47
r9c7 = 47
Staring with r2c6 as alpha and following only the digit 4 (which means coloring!!!):
r2c6 = 4 r2c7 <> 4 r9c7 = 4
r2c6 = 4 r3c5 <> 4 r9c5 = 4

And this is excluding 4 from r2c6, because of contradiction in row 9.

Nice one, thank you.

see u next week,
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