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"Nightmare" for Thursday, 9 March, 2006

 
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Thu Mar 09, 2006 3:58 pm    Post subject: "Nightmare" for Thursday, 9 March, 2006 Reply with quote

This puzzle isn't nearly as hard as the "zen" sudoku I posted here yesterday, but it's still plenty tough. I found two different "5-star constellations" before I was able to solve it.
Code:
.6..2....
..84..7.1
..16....2
7..1.....
..9.7.6..
.....4..3
9....53..
3.5..24..
....4..8.

Enjoy! dcb

PS In reworking this puzzle I noticed that the first "5-star constellation" I found was not really necessary -- there was a triplet {7, 8, 9} that would have served the same purpose, if I had only noticed it.
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keith



Joined: 19 Sep 2005
Posts: 3175
Location: near Detroit, Michigan, USA

PostPosted: Thu Mar 09, 2006 10:27 pm    Post subject: Color me again! Reply with quote

David,

I found that early on there is a coloring on <7> which excludes that value from R9C3. This is a big help. Then, the puzzle can be solved via an X-wing on <3> (which also appears early), and the last step is an XY-wing on <9>. (After that, all moves are forced.)

Keith
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someone_somewhere



Joined: 07 Aug 2005
Posts: 275
Location: Munich

PostPosted: Sun Mar 12, 2006 2:51 pm    Post subject: Reply with quote

Hi,
Just tried this one, in order to check that I am still alive ...

I foud for digit 3 a X-Wing on Column in: r2c2 r2c6 r5c2 r5c6
so I could eliminate it from: r3c2, r3c6, r4c2, r4c6, r9c6
and so 3 is in r9c4 as Unique Horizontal.

Now I excluded 6 from r4c3, because it would otherwise force a 6 in r9c1 and r9c6.

Followed by 9 not in r3c5 because of an XY-wing (that I leave to you to find) and by 9 not in r4c6 because of an other similar XY-wing.

Finally, I excluded 1 from r6c2, because it would give a contradiction on row with r9c1 and r9c7 for digit 1.

P.S. galaxies behind the "zen" one !!!

see u,
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