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One from Australia

 
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Mon Apr 14, 2008 12:18 am    Post subject: One from Australia Reply with quote
This is the Tough from Feb. 18, 2008. An interesting one, at least to me.

Code:

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

Play this puzzle online at the Daily Sudoku site
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
PostPosted: Mon Apr 14, 2008 12:48 pm    Post subject: Reply with quote
Yes, it is interesting.

This position came up:

Code:
+---------------------------------------+
| 6  79   8    | 2   35  35  | 79  1  4 |
| 15 12+5 27+1 | 9   6   4   | 35  37 8 |
| 3  45   49+5 | 7   8   1   | 59  6  2 |
-----------------------------------------
| 2  3    57   | 48  1   57  | 48  9  6 |
| 8  57   6    | 45  9   37  | 2   34 1 |
| 9  14   14   | 38  2   6   | 38  5  7 |
-----------------------------------------
| 15 6    13   | 35  47  2   | 47  8  9 |
| 4  29   59+2 | 1   57  8   | 6   27 3 |
| 7  8    23   | 6   34  9   | 1   24 5 |
+---------------------------------------+

The BUG+4 makes a couple of eliminations. If any of the non-BUG candidates goes into box 1, r3c2 contains 4. On the other hand, if r8c3 contains 2, r789c3 contain 1, 2 and 3 so r6c3 contains 4. Whichever applies, 4 may be eliminated from r3c3 and r6c2

This gives:

Code:
+----------------------------------------+
| 6   79   8    | 2   35  35  | 79  1  4 |
| 15  25   127  | 9   6   4   | 35  37 8 |
| 3   4    59   | 7   8   1   | 59  6  2 |
------------------------------------------
| 2   3    57   | 48  1   57  | 48  9  6 |
| 8   57   6    | 45  9   37  | 2   34 1 |
| 9   1    4    | 38  2   6   | 38  5  7 |
------------------------------------------
| 15  6    13   | 35  47  2   | 47  8  9 |
| 4   29   259  | 1   57  8   | 6   27 3 |
| 7   8    23   | 6   34  9   | 1   24 5 |
+----------------------------------------+


The XY-Wing for (79) pivoted on r1c2 with pincers r3c3 and r5c2 then eliminates 5 from r2c2 and r5c3, solving the puzzle.

There’s no particular reason why a BUG should not be followed by another trick but I can’t recall coming across it before.

Thanks, Marty.

Steve
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Mon Apr 14, 2008 1:30 pm    Post subject: Reply with quote
Nice puzzle.

I found a UR, xy-wing, M-wing 34 (2 times), coloring 5, double linked w-wing 57 (1 strong link for 5, 3 strong links for 7) with transports for 5.
Finally i needed a 7-cell xy-chain (r2c7<>5) to finish off.

Ah - nice solution, Steve !
[Added:] How did you eliminate 7 from r2c2 and 9 from r3c2 ?
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England
PostPosted: Mon Apr 14, 2008 3:50 pm    Post subject: Reply with quote
To make the eliminations independently, you could use the XY-chains:

-7- r2c8 -3- r5c8 -4- r5c4 -5- r5c2 -7-
-9- r3c7 -5- r2c7 -3- r2c8 -7- r8c8 -2- r8c2 -9-

In practice, I doubt that this is necessary. Suppose you start from here:

Code:
+----------------------------------------+
| 6  79    8    | 2   35  35  | 79  1  4 |
| 15 12+57 27+1 | 9   6   4   | 35  37 8 |
| 3  45+9  49+5 | 7   8   1   | 59  6  2 |
------------------------------------------
| 2  3     57   | 48  1   57  | 48  9  6 |
| 8  57    6    | 45  9   37  | 2   34 1 |
| 9  14    14   | 38  2   6   | 38  5  7 |
------------------------------------------
| 15 6     13   | 35  47  2   | 47  8  9 |
| 4  29    59+2 | 1   57  8   | 6   27 3 |
| 7  8     23   | 6   34  9   | 1   24 5 |
+----------------------------------------+

I think you will find that any of the non-BUG candidates places 4 in r6c3.

I actually worked from a BUG+6 but simplified the diagram a little because the detail of the BUG obscured the point that caught my interest.

Steve
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Mon Apr 14, 2008 4:00 pm    Post subject: Reply with quote
I had a couple of ERs, a UR, and XY-Wing. Then the M-Wing used once, then again after extending a pincer two more cells. But after that, I needed Medusa to finish up.
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Mon Apr 14, 2008 5:19 pm    Post subject: Reply with quote
Steve R wrote:
I actually worked from a BUG+6 ...
Great, never seen/tried such a thing.
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