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April 25 DB

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Apr 25, 2009 1:47 pm    Post subject: April 25 DB Reply with quote
I found this April 25 DB tough.

A SOLUTION: an xy-chain eliminates the <2> in R3C9, then an xy-wing eliminates <6> in R3C5, leaving a BUG+1 for a <6> in R2C7. Gotta be an easier way!

Earl

Code:

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

Play this puzzle online at the Daily Sudoku site
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Apr 25, 2009 4:45 pm    Post subject: Reply with quote
A fairly long XY-Chain eliminated the 5 from r7c5 and that set up a puzzle-ending W-Wing on 16.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Sat Apr 25, 2009 9:45 pm    Post subject: Reply with quote
I gree with Marty that a xy-chain may be the most direct move to a solution.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Wed Apr 29, 2009 5:11 pm    Post subject: Reply with quote
After basics:
Code:
+----------------+----------------+----------------+
| 5    8    47   |1-26  3   1-27  | 46c  9    26d  |
| 34   2    1    | 68   46   9    | 4678 5    367  |
| 9    6    347  | 28a  45   257  | 48b  1   -23   |
+----------------+----------------+----------------+
| 2    4    5    | 7    9    8    | 3    6    1    |
| 6    3    9    | 5    1    4    | 2    7    8    |
| 7    1    8    | 3    2    6    | 5    4    9    |
+----------------+----------------+----------------+
| 134  9    234  | 126  56   1235 | 17   8    57   |
| 13   7    36   | 4    8    135  | 9    2    56   |
| 8    5    26   | 9    7    12   | 16   3    4    |
+----------------+----------------+----------------+

I used two four-cell chains (extended XY-wings), an XY-wing, and then a W-wing (instead of the BUG) to finish it.

Edit: abcd is a chain with pincers <2> and makes the eliminations shown. That reveals a W-wing 16 12 12 16 that removes <6> from R1C7 and solves the puzzle.

Keith
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