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Multi-step VH (BBsh 020309)

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keith

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

Posted: Wed Feb 04, 2009 11:02 pm Post subject: Multi-step VH (BBsh 020309)

This one gets to the point, with five boxes solved, very quickly:

Code:

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

Play this puzzle online at the Daily Sudoku site

After basics, see if you can find the rectangular XY-cycle / loop. Very cool! (This is the Brain Basher super hard from yesterday, Feb. 3.)

Keith

daj95376

Joined: 23 Aug 2008
Posts: 3854

Posted: Wed Feb 04, 2009 11:52 pm Post subject:

Withdrawn! Last edited by daj95376 on Thu Feb 05, 2009 1:51 am; edited 1 time in total

keith

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

Posted: Thu Feb 05, 2009 12:25 am Post subject:

daj95376 wrote:

Don't read my solution until after you find it for yourself.

Couldn't wait wrote:

[c3] __ 32-26 __ aligns with ...
[c7] __ 31-16 __ ... six eliminations

And, how many bivalue cells are there that form a rectangle? Once you know to look, it should be easy to find.

To tell the truth, I did not notice it until after I has done an X-wing and a couple of XY-wings. By then, there were only three elininations in two candidates.

Keith

daj95376

Joined: 23 Aug 2008
Posts: 3854

Posted: Thu Feb 05, 2009 1:24 am Post subject:

keith wrote:

And, how many bivalue cells are there that form a rectangle? Once you know to look, it should be easy to find.

You are quite correct!!!

I should have made it clear that I make no claims to knowing that it was present or that it was easy to locate.

All I wanted to do was share the simple alignment method that makes them visible to me. This approach works in PMs with many bivalue cells present.

All other credit goes to you!!! I did not mean to take away from your effort.

BTW: I couldn't get any of my eliminations to advance the puzzle past needing the steps that you performed before getting to the XY-Loop. So, your effort was not in vain!!!

keith

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

Posted: Thu Feb 05, 2009 2:09 am Post subject:

Danny,

Quote:

All I wanted to do was share the simple alignment method that makes them visible to me.

And, I agree! I really intended this as a tutorial, waiting to see how others might recognize and discover these loops.

Loops aside, it takes an X-wing, and four XY-wings to crack this one. The last step could be a BUG+1 or XYZ-wing.

Keith

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