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Dec 20 DB

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Dec 20, 2008 2:01 pm    Post subject: Dec 20 DB Reply with quote
The December 20 DB made me work. I had to use an xy-chain to eliminate some 1's, which opened a skyscraper in 1's to finish it. I could not see a more direct route.

Earl

Code:

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

Play this puzzle online at the Daily Sudoku site

Last edited by Earl on Sat Dec 20, 2008 2:31 pm; edited 1 time in total
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
PostPosted: Sat Dec 20, 2008 2:25 pm    Post subject: Reply with quote
My first move after basics completed the puzzle:
Quote:
ER <1> in b5 with strong link r9; delete r5c2

Ted
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat Dec 20, 2008 9:03 pm    Post subject: Reply with quote
Another pseudo-cell finds a four-cell chain:
Code:
+----------------+----------------+----------------+
| 7    2    9    | 1    356  35b  | 8    4    56c  |
| 16   4    156  | 8    2    7    | 9    3    156  |
| 168  3    1568 | 4    56   9    | 126  12   7    |
+----------------+----------------+----------------+
| 5    7    168  | 2   -18   4    | 3    9    16d  |
| 4    16   1368 | 7    9    13a  |-156 -158  2    |
| 138  9    2    | 5    138  6    | 7    18   4    |
+----------------+----------------+----------------+
| 136  156  136  | 9    4    125  | 125  7    8    |
| 9    8    4    | 6    7    125  | 125  125  3    |
| 2    15   7    | 3    15   8    | 4    6    9    |
+----------------+----------------+----------------+
ab are a pseudo-cell <15>, so ab c d is an extended xy-wing. Any cell that sees both a and d cannot be <1>.

Another way to look at this is as follows. Either

d is <1>, or
d is <6>, which forces <1> in a.

Then, a skyscraper takes out <1> in R5C2 to solve it. (Sounds like it is the same solution Earl found.)

Otherwise:

The ER is really cool!

There is a half M-wing that takes out <6> in R23C3.
A W-wing takes out <1> in R7C6.
Then, the same wing with transport takes out <1> in R9C2.


Keith
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