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March 16 - VH

 
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prakash



Joined: 02 Jan 2008
Posts: 67
Location: New Jersey, USA

PostPosted: Sun Mar 16, 2008 12:51 am    Post subject: March 16 - VH Reply with quote

Very straight forward. An XY wing 58-89-59 cracked open the puzzle.
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Stanley P



Joined: 27 Feb 2008
Posts: 20
Location: Tennessee, USA

PostPosted: Sun Mar 16, 2008 6:09 am    Post subject: Reply with quote

Same xy-wing did it for me.
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales

PostPosted: Sun Mar 16, 2008 9:17 am    Post subject: Reply with quote

And me!

(Pivot on R6C1 for anyone who doesn't see it). Smile

John
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Earl



Joined: 30 May 2007
Posts: 595
Location: Victoria, KS

PostPosted: Sun Mar 16, 2008 11:50 am    Post subject: March 16 Reply with quote

Just one more step.

Earl


Code:

+-------------+----------+------------+
| 578 3   248 | 6  458 1 | 28  57 9   |
| 1   47  248 | 3  458 9 | 268 57 26  |
| 58  6   9   | 25 258 7 | 1   3  4   |
+-------------+----------+------------+
| 2   5   3   | 1  6   4 | 7   9  8   |
| 79  47  46  | 8  59  2 | 56  1  3   |
| 89  18  168 | 59 7   3 | 4   2  56  |
+-------------+----------+------------+
| 6   9   7   | 4  12  5 | 3   8  12  |
| 3   128 158 | 29 129 6 | 25  4  7   |
| 4   12  15  | 7  3   8 | 9   6  125 |
+-------------+----------+------------+

Play this puzzle online at the Daily Sudoku site
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Mar 16, 2008 1:28 pm    Post subject: Reply with quote

Looked for ERs and URs but couldn't find any. I have tremendous difficulty with xy wings. Solved this one by a method that often works for me - screwed up and got lucky!!!
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prakash



Joined: 02 Jan 2008
Posts: 67
Location: New Jersey, USA

PostPosted: Sun Mar 16, 2008 1:33 pm    Post subject: Reply with quote

I was always assume that the XY wing would not be in a regular shape (square or rectangle). Having one so straight forward was a challenge to find.

Prakash
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Marty R.



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

PostPosted: Sun Mar 16, 2008 4:20 pm    Post subject: Reply with quote

This puzzle required no steps for me. Just started the initial scan of rows and my eraser never stopped until it was done.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sun Mar 16, 2008 8:32 pm    Post subject: Reply with quote

Quote:
This puzzle required no steps for me. Just started the initial scan of rows and my eraser never stopped until it was done.


Nay! Methinks you erred like what I did. I did it again and one definitely has to resort to clever VH stuff.
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Marty R.



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

PostPosted: Sun Mar 16, 2008 9:39 pm    Post subject: Reply with quote

cgordon wrote:
Quote:
This puzzle required no steps for me. Just started the initial scan of rows and my eraser never stopped until it was done.


Nay! Methinks you erred like what I did. I did it again and one definitely has to resort to clever VH stuff.

Craig, since your credentials are unimpeachable, I tried it again, this time online rather than P&P and you may be right. Basics only got me this far:

Code:

+-------------+----------+------------+
| 578 3   248 | 6  458 1 | 28  57 9   |
| 1   47  248 | 3  458 9 | 268 57 26  |
| 58  6   9   | 25 258 7 | 1   3  4   |
+-------------+----------+------------+
| 2   5   3   | 1  6   4 | 7   9  8   |
| 79  47  46  | 8  59  2 | 56  1  3   |
| 89  18  168 | 59 7   3 | 4   2  56  |
+-------------+----------+------------+
| 6   9   7   | 4  12  5 | 3   8  12  |
| 3   128 158 | 29 129 6 | 25  4  7   |
| 4   12  15  | 7  3   8 | 9   6  125 |
+-------------+----------+------------+

Play this puzzle online at the Daily Sudoku site

The deadly pattern on 28 in boxes 1 and 3 can be broken up by a 6 in r2c7 or a 4 in r1c3 or r2c3. All three result in a 6 in r5c3 and that solves it. I'll probably take a look at other methods as well.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Mar 17, 2008 11:28 am    Post subject: Reply with quote

Quote:
The deadly pattern on 28 in boxes 1 and 3 can be broken up by a 6 in r2c7 or a 4 in r1c3 or r2c3. All three result in a 6 in r5c3


Marty: I kept staring at these 4 cells because they look like a UR but they don't fit in to the Types given in the Sudoku technique references. There are two options - is it a pair of 4s or a 6. So really you have to do a bit of trial and error - don't you think?? Nonetheless I do see these patterns now and again and I think they should be acknowledged - i.e., given a label.

Just a thought.
Craig
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Marty R.



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

PostPosted: Mon Mar 17, 2008 3:42 pm    Post subject: Reply with quote

Quote:
There are two options - is it a pair of 4s or a 6. So really you have to do a bit of trial and error - don't you think??

Yes, I do think there's some trial-and-error there, but there are degrees of trial-and-error and this ranks above something like picking a bivalue cell and testing it for a forcing chain.

The deadly pattern was the first thing I noticed; when I looked at it later, the 89-58-59 XY-Wing solves the puzzle.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Mon Mar 17, 2008 10:08 pm    Post subject: Reply with quote

Quote:
Yes, I do think there's some trial-and-error there, but there are degrees of trial-and-error and this ranks above something like picking a bivalue cell and testing it for a forcing chain.


Sadly I think this Post will get lost by the wayside - because often I see many UR looking patterns that have too many numbers for a UR solution. For example - a 458, 458, 458, 4589. If I were in a Sudoku competion where speed was involved - I would look for these patterns - and find a quick chain. As did you.
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