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andras
Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales
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 Posted: Tue Jan 22, 2008 7:54 am Post subject: Jan 22 VH |
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Is it just me or was it more like a Medium? No special tricks needed at all. 
John |
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livemuse82
Joined: 22 Jan 2008
Posts: 3
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| Posted: Tue Jan 22, 2008 1:35 pm Post subject: Next Move? |
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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
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| Posted: Tue Jan 22, 2008 2:10 pm Post subject: |
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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
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| Posted: Tue Jan 22, 2008 2:22 pm Post subject: |
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| 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 |
+--------------+-----------+------------+
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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
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| Posted: Tue Jan 22, 2008 3:44 pm Post subject: |
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| 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
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| Posted: Tue Jan 22, 2008 4:37 pm Post subject: |
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| I used the XY-Wing in Ravel's grid and the W-Wing. |
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livemuse82
Joined: 22 Jan 2008
Posts: 3
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| Posted: Tue Jan 22, 2008 5:04 pm Post subject: Thanks! |
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| 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
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| Posted: Tue Jan 22, 2008 5:38 pm Post subject: |
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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
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| Posted: Tue Jan 22, 2008 6:26 pm Post subject: |
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| 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
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| Posted: Tue Jan 22, 2008 9:52 pm Post subject: |
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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
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| Posted: Wed Jan 23, 2008 12:10 am Post subject: W Wing |
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| 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
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| Posted: Wed Jan 23, 2008 9:08 am Post subject: Re: W Wing |
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| 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 . |
+-------------------+
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>>> 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
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>>> 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
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>>> 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: 3355
Location: near Detroit, Michigan, USA
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| Posted: Wed Jan 23, 2008 9:10 am Post subject: |
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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
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| Posted: Wed Jan 23, 2008 10:36 am Post subject: |
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| 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: 3355
Location: near Detroit, Michigan, USA
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| Posted: Wed Jan 23, 2008 11:57 pm Post subject: |
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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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