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Not so difficult?

 
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Mon Jan 21, 2008 10:16 pm    Post subject: Not so difficult? Reply with quote

Based on the rating, I expected less than 30 min and an XY-wing or two. I eventually resorted to Medusa coloring (which works quite nicely).

Any better ideas?

Code:
Puzzle: M4447344sh(8)
+-------+-------+-------+
| . . . | . 6 . | . . . |
| 5 . . | 4 . 1 | 2 . . |
| . 9 . | 2 . 7 | . . . |
+-------+-------+-------+
| . 6 7 | . . . | 4 9 . |
| 1 . . | 7 . 8 | . . 5 |
| . 5 9 | . . . | 7 3 . |
+-------+-------+-------+
| . 4 . | 3 . 2 | . . . |
| . . . | 6 . 4 | 9 . . |
| . . . | . 8 . | . 1 . |
+-------+-------+-------+


Keith
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Mon Jan 21, 2008 10:37 pm    Post subject: Easy Reply with quote

Keith,

It can also be solved with an long xy-chain (not very sophisticated), pincers (6) at R2C3 and R9C1.
But it would be very instructive for many of us if you would show the specifics of your solution with Medussa Coloring. Thanks

Earl
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Asellus



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

PostPosted: Tue Jan 22, 2008 12:33 am    Post subject: Reply with quote

Earl,

I'll take the liberty of posting a Medusa solution. In the grid after basics, the <6>s and <7>s both have lots of strong links and bivalues. So, I start by coloring <6>s and the digits with which they form bivalues:
+---------------+--------+----------------+

| 47 12 123 | 8 6 9 | 15 45 37 |
| 5 78 68 | 4 3 1 | 2 67 9 |
| 46 9 13 | 2 5 7 | 18 48 36 |
+---------------+--------+----------------+
| 8 6 7 | 5 2 3 | 4 9 1 |
| 1 3 4 | 7 9 8 | 6 2 5 |
| 2 5 9 | 1 4 6 | 7 3 8 |
+---------------+--------+----------------+
| 9 4 158 | 3 17 2 | 58 5678 67 |
| 3 18 158 | 6 17 4 | 9 578 2 |
| 67 27 26 | 9 8 5 | 3 1 4 |
+---------------+--------+----------------+

Next, I can extend the coloring to <2>s and <3>s and any bivalue companions that result:
+-----------------+--------+----------------+

| 47 12 123 | 8 6 9 | 15 45 37 |
| 5 78 68 | 4 3 1 | 2 67 9 |
| 46 9 13 | 2 5 7 | 18 48 36 |
+-----------------+--------+----------------+
| 8 6 7 | 5 2 3 | 4 9 1 |
| 1 3 4 | 7 9 8 | 6 2 5 |
| 2 5 9 | 1 4 6 | 7 3 8 |
+-----------------+--------+----------------+
| 9 4 158 | 3 17 2 | 58 5678 67 |
| 3 18 158 | 6 17 4 | 9 578 2 |
| 67 27 26 | 9 8 5 | 3 1 4 |
+-----------------+--------+----------------+

Notice that we have a Medusa Wrap: there are two green digits in the cell r1c3.
So, all green values are false and all red values true.
This solves the puzzle.
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Marty R.



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

PostPosted: Tue Jan 22, 2008 12:58 am    Post subject: Reply with quote

Earl,

I have no idea of what you know or don't know about Medusa. If you're not familiar with it, start here with Keith's explanation of the basics.

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2171&highlight=crayola&sid=567e97c6a3fc3a73cec71dc796d75fd7

Then ask questions, like I did, until you get it. Then read Asellus' explanation of extended Medusa in the Solving Techniques forum.

I've learned a number of valuable techniques in the last six months, but so far it looks like Medusa is the most powerful of the bunch. You won't regret having this one in the old arsenal.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Tue Jan 22, 2008 1:29 am    Post subject: Reply with quote

The beauty of Medusa is that she lays out an entire net of possibilities.

If you'd like a short cut, start in R9C2: 2 Green, 7 Red. I count only 5 moves to R1C3, both <23> are Green, Red must be true.

Keith
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Tue Jan 22, 2008 9:07 am    Post subject: Reply with quote

Code:
 *------------------------------------------*
 | 47  12  123  | 8  6   9  | 15  45    37  |
 | 5   78  68   | 4  3   1  | 2   67    9   |
 | 46  9  #13   | 2  5   7  | 18  48   #36  |
 |--------------+-----------+---------------|
 | 8   6   7    | 5  2   3  | 4   9     1   |
 | 1   3   4    | 7  9   8  | 6   2     5   |
 | 2   5   9    | 1  4   6  | 7   3     8   |
 |--------------+-----------+---------------|
 | 9   4  -158  | 3 #17  2  | 58  5678 #67  |
 | 3   18  158  | 6  17  4  | 9   578   2   |
 | 67  27  26   | 9  8   5  | 3   1     4   |
 *------------------------------------------*
Either r3c3=1 or r3c3=3 => r3c9=6 => r7c9=7 => r7c5=1
Code:
 *---------------------------------------*
 | 47 -12 #123  | 8  6  9  | 15  45  37  |
 | 5   78  68   | 4  3  1  | 2   67  9   |
 | 46  9   13   | 2  5  7  | 18  48  36  |
 |--------------+----------+-------------|
 | 8   6   7    | 5  2  3  | 4   9   1   |
 | 1   3   4    | 7  9  8  | 6   2   5   |
 | 2   5   9    | 1  4  6  | 7   3   8   |
 |--------------+----------+-------------|
 | 9   4   58   | 3  1  2  | 58  67  67  |
 | 3  @18 #158  | 6  7  4  | 9   58  2   |
 | 67  27  26   | 9  8  5  | 3   1   4   |
 *---------------------------------------*

From the BUG either r1c3=1 or r8c3=8 => r9c2=1
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dejsmith



Joined: 23 Oct 2005
Posts: 42

PostPosted: Tue Jan 22, 2008 9:49 pm    Post subject: Reply with quote

Marty

"...so far it looks like Medusa is the most powerful of the bunch. You won't regret having this one in the old arsenal"

Thanks for getting me "off my duff" to finally examine Medusa!

And Keith & Asellus, thanks for your explanations. After also studying Rudd's explanation & Dr Hanson's, I am trying this now & getting it.

As you know I am always a few days behind & that is why I do not contribute much; but, to tell you the truth, Medusa almost makes me feel like I am cheating. It works very well with my pencil marking routine! I look forward to trying to use it often.

Dave
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Tue Jan 22, 2008 10:09 pm    Post subject: Reply with quote

very powerful indeed... after all, one glare and you were a statue made of stone. and !! how many women can wake up and deal with that hair everyday?? she did it.
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