dailysudoku.com

[keith]

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?

[Earl]

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

[Asellus]

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.

[Marty R.]

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.

[keith]

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

[ravel]

[dejsmith]

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

[storm_norm]

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.