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Freep Oct 26

 
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Oct 27, 2007 5:21 pm    Post subject: Freep Oct 26 Reply with quote
Harder than "Very Hard", I believe.
Code:
Puzzle: FP102607
+-------+-------+-------+
| 8 9 . | . . . | . . . |
| . . 5 | . 8 . | 1 . . |
| . . 2 | 7 . 6 | 3 . 8 |
+-------+-------+-------+
| . 2 . | . . . | . 3 . |
| 9 . . | 3 . 8 | . . 2 |
| . 8 . | . . . | . 1 . |
+-------+-------+-------+
| 6 . 1 | 5 . 3 | 2 . . |
| . . 8 | . 7 . | 5 . . |
| . . . | . . . | . 7 1 |
+-------+-------+-------+

Keith
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Oct 27, 2007 6:22 pm    Post subject: Freep Reply with quote
Keith,

I saw a skyscraper in <9>'3, then an xy-wing (7) another xy-wing (9) and then just singles. Is there a neater way?

Earl
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Oct 27, 2007 8:10 pm    Post subject: Reply with quote
I used the skyscraper on <9>, then an X-wing on <7> and coloring on <6>, as I recall. If you don't see the skyscraper, you'll have a tough time of it.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Oct 27, 2007 9:44 pm    Post subject: Reply with quote
There's an alternate solution. After the basics and failing to spot any XY- or XYZ-Wings, this was the position:

Code:

+-----------+---------------+---------------+
| 8  9  67  | 124 3    1245 | 467 2456 4567 |
| 37 36 5   | 249 8    249  | 1   2469 4679 |
| 4  1  2   | 7   59   6    | 3   59   8    |
+-----------+---------------+---------------+
| 1  2  467 | 469 4569 4579 | 8   3    4567 |
| 9  56 467 | 3   1    8    | 467 456  2    |
| 57 8  3   | 246 2456 2457 | 9   1    4567 |
+-----------+---------------+---------------+
| 6  7  1   | 5   49   3    | 2   8    49   |
| 2  4  8   | 169 7    19   | 5   69   3    |
| 35 35 9   | 8   246  24   | 46  7    1    |
+-----------+---------------+---------------+

Play this puzzle online at the Daily Sudoku site

An Empty Rectangle on 9, with the ERI in r7c8 solves r7c5=4. The eliminations therefrom expose an XY-Wing on 56-57-67, which eliminates one 7 and doesn't seem to help very much. However, then coloring one of the pincers allows elimination of another 7 which solves a cell, after which the eliminations lead to a BUG+1, solving r2c4=9.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Oct 27, 2007 10:24 pm    Post subject: Reply with quote
Marty,

Cool! The skyscraper (strong links on <9>) can be observed in R37. It takes out <9> in R2C9.

Then, a few basic moves lead to coloring opportunities or XY-wings which solve the puzzle.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Oct 27, 2007 11:44 pm    Post subject: Reply with quote
Quote:
The skyscraper (strong links on <9>) can be observed in R37. It takes out <9> in R2C9.


Yep. That's basically the same result as the ER, since after a move or two, the same 4 is placed in r7c5 that the ER placed.

For some reason, I despise looking for X-Wings (which is where I find my skyscrapers), so I look for everything else before looking for them as a last resort.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Sun Oct 28, 2007 1:05 am    Post subject: Reply with quote
I too started with the Skyscraper on <9>. After that, there's a Skyscraper on <6> in C27 that removes <6> from R1C3 and R2C9, leading to the suddenly ever so popular BUG+1.
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Sun Oct 28, 2007 9:38 am    Post subject: Reply with quote
I had about the same sequence as Marty, but after the xy-wing (which at first glance didn't seem to do much) there was a hidden single 7 at r5c7 and the puzzle solved easily from there.

one color wing, one xy wing. just right for a sunday ...
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