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Feb 2 DB

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Feb 02, 2008 2:01 pm    Post subject: Feb 2 DB Reply with quote
This Goundhog DB kept me in the dark until I used an xy-chain to eliminate the 4 in R1C8 and see daylight.

Earl


Code:

+-------+-------+-------+
| . . . | 1 . 6 | . . . |
| 7 5 . | . . . | . . . |
| 8 . 4 | . . 3 | . . . |
+-------+-------+-------+
| 4 9 . | . 3 . | 2 . . |
| . . 6 | . . . | 9 . . |
| . . 5 | . 9 . | . 6 4 |
+-------+-------+-------+
| . . . | 2 . . | 6 . 9 |
| . . . | . . . | . 5 8 |
| . . . | 4 . 1 | . . . |
+-------+-------+-------+

Play this puzzle online at the Daily Sudoku site
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Feb 02, 2008 6:11 pm    Post subject: Reply with quote
Quote:
This Goundhog DB kept me in the dark until I used an xy-chain to eliminate the 4 in R1C8 and see daylight.

History says we'll get six more weeks of winter here regardless of what the rodent sees.

Basic Medusa trapped a couple of candidates which broke it open. The grid looked like it had high potential for XY- and XYZ-Wings, but I couldn't find any, nor were there any ERs that I could see.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Feb 02, 2008 8:41 pm    Post subject: Reply with quote
Medusa 4 - 1 - 7 - 5 - 4 solves R1C8 as <8>, solving the puzzle. One chain is R1C5 R9C5 R7C6 R4C6 R4C8 R7C8

Code:
+-------------+-------------+-------------+
| 9   23  23  | 1  4r5g 6   | 458 -48 7   |
| 7   5   1   | 9   24  8   | 34  234 6   |
| 8   6   4   | 57  27  3   | 15  9   12  |
+-------------+-------------+-------------+
| 4   9   8   | 6   3  5r7g | 2  1g7r 15  |
| 23  237 6   | 578 1   4   | 9   378 35  |
| 13  137 5   | 78  9   2   | 378 6   4   |
+-------------+-------------+-------------+
| 135 134 37  | 2   8  5g7  | 6  1r4g 9   |
| 126 124 27  | 3   67  9   | 14  5   8   |
| 56  8   9   | 4  5r6  1   | 37  237 23  |
+-------------+-------------+-------------+


Keith
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dejsmith



Joined: 23 Oct 2005
Posts: 42
PostPosted: Wed Feb 06, 2008 10:33 pm    Post subject: Question for Keith Reply with quote
Keith

I cannot understand how you got the 5 out of R3C5. My candidates' profile is the same as yours except for that (I have R3C5=257). And without eliminating that 5, I cannot figure out how to make the Medusa string work. I apologize in advance if it is something simple I just cannot see; but I am trying to expand my solving techniques.

Dave
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Thu Feb 07, 2008 2:14 am    Post subject: Reply with quote
Dave,

I can only think that I made a lucky mistake. I was solving with pencil and paper, so I do not know how I reached the position I posted.

You might note that the <57> cells possibly form W-wings and M-wings. I am inclined to recall I used a flightless XY-wing plus coloring, but I cannot now see it.

I have not yet looked at how Medusa works on this grid:

Code:
+-------------+-------------+-------------+
| 9   23  23  | 1   45  6   | 458 48  7   |
| 7   5   1   | 9   24  8   | 34  234 6   |
| 8   6   4   | 57  257 3   | 15  9   12  |
+-------------+-------------+-------------+
| 4   9   8   | 6   3   57  | 2   17  15  |
| 23  237 6   | 578 1   4   | 9   378 35  |
| 13  137 5   | 78  9   2   | 378 6   4   |
+-------------+-------------+-------------+
| 135 134 37  | 2   8   57  | 6   14  9   |
| 126 124 27  | 3   67  9   | 14  5   8   |
| 56  8   9   | 4   56  1   | 37  237 23  |
+-------------+-------------+-------------+

Keith

(Whose normal 35 minute commute took 2.5 hours in the snowstorm.)
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Thu Feb 07, 2008 7:55 am    Post subject: Reply with quote
This is the full (but not extended) Medusa coloring, starting at r4c6.
I chose r4c6 because both 5 and 7 have a lot of connected strong liks.



It is clear that neither r1c8 nor r2c7 can be 4.

It is also obvious that Medusa coloring can take quite some time.
Not obvious fom the picture but in my experience: it is terribly error prone.
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Thu Feb 07, 2008 12:20 pm    Post subject: Re: Question for Keith Reply with quote
dejsmith wrote:
I cannot understand how you got the 5 out of R3C5.
You can see it as transported M-wing.
Code:
 *-----------------------------------------------*
 | 9    23   23  | 1   A45   6   |B458  48   7   |
 | 7    5    1   | 9    24   8   | 34   234  6   |
 | 8    6    4   |B57   2-57 3   |A15#  9   @12  |
 |---------------+---------------+---------------|
 | 4    9    8   | 6    3   B57  | 2    17  A15# |
 | 23   237  6   |A578  1    4   | 9    378  35  |
 | 13   137  5   | 78   9    2   | 378  6    4   |
 |---------------+---------------+---------------|
 | 135  134  37  | 2    8    57  | 6    14   9   |
 | 126  124  27  | 3    67   9   | 14   5    8   |
 | 56   8    9   | 4    56   1   | 37   237  23  |
 *-----------------------------------------------*
The 15's are connected by the strong links for 1 via r3c9. So either both are 1 or both are 5.
Now with the strong link for 5 in row 4 we have one of r3c7 and r4c6 must be 5.
Transport r3c7 to r1c5 cia r1c7 (2 strong links) and transport r4c6 to r3c4 via r5c4 => one of r1c5 and r3c4 must be 5.
Code:
 *-----------------------------------------------*
 | 9    23   23  | 1    45   6   | 458  48   7   |
 | 7    5    1   | 9    24   8   | 34   234  6   |
 | 8    6    4   | 57   257  3   | 15   9    12  |
 |---------------+---------------+---------------|
 | 4    9    8   | 6    3    57  | 2    17   15  |
 | 23   237  6   | 578  1    4   | 9    378  35  |
 |#13  #137  5   | 78   9    2   | 378  6    4   |
 |---------------+---------------+---------------|
 |#135 #134  37  | 2    8    57  | 6    14   9   |
 | 126  124  27  | 3    67   9   | 14   5    8   |
 | 56   8    9   | 4    56   1   | 37   237  23  |
 *-----------------------------------------------*
I solved it from the UR13:
r7c2=4 => r8c8=1 => r4c8=7
r7c1=5 => r7c6=7 => r4c6<>7 => r4c8=7
r6c2=7 => r5c12=23 => r5c9=5 => r4c9=1 => r4c8=7
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dejsmith



Joined: 23 Oct 2005
Posts: 42
PostPosted: Thu Feb 07, 2008 8:43 pm    Post subject: Reply with quote
"Transported M-wings"???"Flightless XY-wings"??? I guess it is time for me to go back to school. I found that UR quite imaginative; however, seeing it myself will take the same kind of discipline I am trying to develop for Medusas. Thanks to all.

Dave
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Thu Feb 07, 2008 8:55 pm    Post subject: Reply with quote
Quote:
You can see it as transported M-wing.


Ravel,

Thank you, that is how I did it.

By the way, that same elimination of <5> in R3C5 is made by the Medusa coloring above. R3C5 has both red and green. The other candidate can be eliminated.

Keith
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