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Jan 22 VH

 
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andras



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

PostPosted: Tue Jan 22, 2008 7:54 am    Post subject: Jan 22 VH Reply with quote

Is it just me or was it more like a Medium? No special tricks needed at all. Smile

John
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livemuse82



Joined: 22 Jan 2008
Posts: 3

PostPosted: Tue Jan 22, 2008 1:35 pm    Post subject: Next Move? Reply with quote

Can anyone help with the next move?

Code:

+-------------+-----------+------------+
| 7   8  3    | 4  26  1  | 5   9  26  |
| 15  4  125  | 9  7   56 | 23  8  236 |
| 9   25 6    | 8  23  35 | 4   7  1   |
+-------------+-----------+------------+
| 2   35 59   | 1  359 8  | 7   6  4   |
| 158 6  1589 | 7  59  4  | 289 3  289 |
| 38  7  4    | 2  369 36 | 89  1  5   |
+-------------+-----------+------------+
| 456 9  25   | 36 48  7  | 1   24 38  |
| 46  1  7    | 36 48  2  | 389 5  389 |
| 348 23 28   | 5  1   9  | 6   24 7   |
+-------------+-----------+------------+
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Asellus



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

PostPosted: Tue Jan 22, 2008 2:10 pm    Post subject: Reply with quote

Hello livemuse82... and welcome!

You might want to look for an XY-Wing. If you aren't sure what that is, do a web search (there are plenty of explanations online). Or, you can post again here for more guidance.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Jan 22, 2008 2:22 pm    Post subject: Reply with quote

Code:
+--------------+-----------+------------+
| 7    8  3    | 4  26  1  | 5   9  26  |
| 15   4  125  | 9  7   56 | 23  8  236 |
| 9    25 6    | 8  23  35 | 4   7  1   |
+--------------+-----------+------------+
| 2   @35 -59  | 1  359 8  | 7   6  4   |
| 158  6  1-589| 7  59  4  | 289 3  289 |
| 38   7  4    | 2  369 36 | 89  1  5   |
+--------------+-----------+------------+
| 456  9 @25   | 36 48  7  | 1   24 38  |
| 46   1  7    | 36 48  2  | 389 5  389 |
| 348 #23 28   | 5  1   9  | 6   24 7   |
+--------------+-----------+------------+
There are 2 xy-wings in the grid. This one will not solve it.
Alternatively you can use a w-wing (23).
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cgordon



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

PostPosted: Tue Jan 22, 2008 3:44 pm    Post subject: Reply with quote

Quote:
....was it more like a Medium? No special tricks needed at all.


John:
I think you may have erred. I needed two xy-wings:
<235> with pivot R9C2
<235> with pivot R3C2
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Marty R.



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

PostPosted: Tue Jan 22, 2008 4:37 pm    Post subject: Reply with quote

I used the XY-Wing in Ravel's grid and the W-Wing.
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livemuse82



Joined: 22 Jan 2008
Posts: 3

PostPosted: Tue Jan 22, 2008 5:04 pm    Post subject: Thanks! Reply with quote

Thanks Asellus and Ravel. I've used the 2 xy wings to solve it. I've never heard of the w-wing. I'll have to learn that one for future use. Does it come up frequently?
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andras



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

PostPosted: Tue Jan 22, 2008 5:38 pm    Post subject: Reply with quote

Well, I've been through my solution again and it all works out for me without any x-wings or anything else; I did it over a single cup of tea before breakfast.

Usually it's my wife who somehow stumbles on a direct route while I'm left analysing for wings and URs! I guess I just got lucky for once!

John
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Marty R.



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

PostPosted: Tue Jan 22, 2008 6:26 pm    Post subject: Reply with quote

Quote:
I've never heard of the w-wing. I'll have to learn that one for future use. Does it come up frequently?

Yes, it does appear fairly frequently and is a valuable component of one's arsenal. If you have identical bivalue cells in different houses and they are connected by a strong link, then the number other than the strong link must be in one or the other bivalue cells, forming a pincer effect like an XY-Wing.

Code:
+--------------+-----------+------------+
| 7    8  3    | 4  26  1  | 5   9  26  |
| 15   4  125  | 9  7   56 | 23  8  236 |
| 9    25 6    | 8  23  35 | 4   7  1   |
+--------------+-----------+------------+
| 2   @35 -59  | 1  359 8  | 7   6  4   |
| 158  6  1-589| 7  59  4  | 289 3  289 |
| 38   7  4    | 2  369 36 | 89  1  5   |
+--------------+-----------+------------+
| 456  9 @25   | 36 48  7  | 1   24 38  |
| 46   1  7    | 36 48  2  | 389 5  389 |
| 348 #23 28   | 5  1   9  | 6   24 7   |
+--------------+-----------+------------+


In this grid, note the 23 cells in r3c5 and r9c2. Also note the strong link on 3 in row 4. Each of the 3s sees one of those 23 cells. Therefore, one or the other of the pairs must contain a 2 and that pincer effect zaps the 2 from r3c2.

I don't know if that's clear, but you definitely want to have this technique at your disposal.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Tue Jan 22, 2008 9:52 pm    Post subject: Reply with quote

mark me down for...
xy-wing {2,3,5} pincers in r3c5 and r4c2 takes out 3 in r4c5
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livemuse82



Joined: 22 Jan 2008
Posts: 3

PostPosted: Wed Jan 23, 2008 12:10 am    Post subject: W Wing Reply with quote

Thank you Marty R. for your thorough and crystal clear explanation of the W Wing. I've definitely added it to my arsenal, although it may take a few VH sudokus for me to get used to using it.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Wed Jan 23, 2008 9:08 am    Post subject: Re: W Wing Reply with quote

livemuse82 wrote:
... it may take a few VH sudokus for me to get used to using it.
You can try this one:
Code:
 
 +-------------------+
 | . 1 . . . . . . . |
 | . . 9 . . . . . . |
 | . 2 . 5 . . 4 3 . |
 | . . . 1 . 6 . . 9 |
 | . 3 . 7 . 8 . . . |
 | . . 8 . . . 1 2 . |
 | 7 4 . . . . . . 2 |
 | . . . . . 5 . . 6 |
 | . . . . . . 3 5 . |
 +-------------------+
>>> play online
You can solve it with 2 w-wings (if you ignore the skyscrapers after the first one).
[Edit:] 2 more - a w-wing is there when you cant get a hint online
[Edit2:] Sorry, i copied a wrong puzzle here.
[Edit3:]This is the right one now.
Code:
 +-------+-------+-------+
 | . . . | . . . | . . . |
 | . . 5 | . 2 . | 3 . . |
 | . 2 . | 6 . 1 | . 8 . |
 +-------+-------+-------+
 | . . 2 | . 5 . | 7 . . |
 | . 5 . | 2 6 7 | . 3 . |
 | . . 8 | . 9 . | 4 . . |
 +-------+-------+-------+
 | . 3 . | 4 . 5 | . 6 . |
 | . . 4 | . 8 . | 9 . . |
 | . . . | . . . | . . . |
 +-------+-------+-------+ gsf
>>> play online
Code:
 +-------+-------+-------+
 | . . . | . . . | . . . |
 | . . 1 | . 2 . | 3 . . |
 | . 6 . | 8 . 4 | . 1 . |
 +-------+-------+-------+
 | . . 2 | . 1 . | 4 . . |
 | . 4 . | 6 7 8 | . 9 . |
 | . . 7 | . 4 . | 8 . . |
 +-------+-------+-------+
 | . 5 . | 7 . 9 | . 3 . |
 | . . 6 | . 3 . | 7 . . |
 | . . . | . . . | . . . |
 +-------+-------+-------+ gsf
>>> play online

Last edited by ravel on Wed Jan 23, 2008 2:32 pm; edited 3 times in total
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keith



Joined: 19 Sep 2005
Posts: 3340
Location: near Detroit, Michigan, USA

PostPosted: Wed Jan 23, 2008 9:10 am    Post subject: Reply with quote

There is an M-wing that solves it.

Basics get you to here:
Code:
+----------------+----------------+----------------+
| 7    8    3    | 4    26   1    | 5    9    26   |
| 15   4    125  | 9    7    56   | 23   8    236  |
| 9    25b  6    | 8    23a  35   | 4    7    1    |
+----------------+----------------+----------------+
| 2    35f  59   | 1   -359  8    | 7    6    4    |
| 158  6    1589 | 7    59   4    | 289  3    289  |
| 38e  7    4    | 2    369  36   | 89   1    5    |
+----------------+----------------+----------------+
| 456  9    25   | 36   48   7    | 1    24   38   |
| 46   1    7    | 36   48   2    | 389  5    389  |
| 348d 23c  28   | 5    1    9    | 6    24   7    |
+----------------+----------------+----------------+

The cells abc are connected by strong links on <2>. a and c have the same value. cd is a strong link on <3> in R9.

1. a is <3>.
2. a is <2>, c is <2>. d must be <3>.
Any cell that sees both a and d cannot be <3>.

That is the M-wing. Not immediately useful.

But, you can color on <3> to e and f. If d is <3>, f is <3>.

Any cell that sees both a and f cannot be <3>. You can make the exclusion in R4C5, which solves the puzzle.

M-wings are explained here:

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2143

Keith

Edit: There is another M-wing on <25> that takes out <5> in R45C3.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Wed Jan 23, 2008 10:36 am    Post subject: Reply with quote

keith wrote:
But, you can color on <3> to e and f. If d is <3>, f is <3>.

You dont even need that. Since there is a strong link for 3 in column 2, also abcf form a M-wing.
Quote:
There is another M-wing on <25> that takes out <5> in R45C3.
I think, this is only a "half" M-wing, (r7c3=2 => r3c2=2, but not vice versa).

It is quite simple to check a grid for (half) M-wings. When it turns out, that a pair is no w-wing, i look, if it can be connected with one color (in both directions). E.g. if you look at the 59's in r4c3 and r5c5, we have r4c3=5 => r5c5=5 (via r4c5). So i look, if there is a strong link for 9 from r5c5. In this case no. If there were one, say to a cell X, it would mean, that r4c3 or X had to be 9.
And r5c5=9 => r4c3=9 (via r5c3), but no strong link for 5 from r4c3. No success here, but it takes just some seconds.

If the pairs are strongly connected like the 23's here, each strong link (for both numbers) from a pair gives you a M-wing.
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keith



Joined: 19 Sep 2005
Posts: 3340
Location: near Detroit, Michigan, USA

PostPosted: Wed Jan 23, 2008 11:57 pm    Post subject: Reply with quote

ravel,

Quote:
You dont even need that. Since there is a strong link for 3 in column 2, also abcf form a M-wing.

Exactly! I missed that. I am not used to how these chains can overlay themselves. (Maybe I am too used to simple coloring which, of course, cannot backtrack in the same column.)

Quote:
I think, this is only a "half" M-wing, (r7c3=2 => r3c2=2, but not vice versa).

Correct, again. I did see this as a half wing, but I neglected to mention that.

By the way, you will find an M-wing by Medusa coloring. I do not think we will find your half-wing. (I'll have to think about it, but in Medusa coloring there are no weak links. At least not in the coloring - they are in the inferences.)

Keith
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