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Stuck Again

 
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Earl



Joined: 30 May 2007
Posts: 546
Location: St Louis MO

PostPosted: Wed Jul 04, 2007 2:11 pm    Post subject: Stuck Again Reply with quote

I can solve this with a forcing chain to a contradiction, which is almost trial and error. Anyone see a "logical" step?

Thanks

Earl

Code:

+------------+-------+------------+
| 16 9  168  | 3 5 7 | 68   2  4  |
| 4  3  2    | 1 8 6 | 9    7  5  |
| 5  67 78   | 9 4 2 | 38   36 1  |
+------------+-------+------------+
| 3  8  16   | 5 7 4 | 16   9  2  |
| 17 56 1457 | 8 2 9 | 1347 36 37 |
| 9  2  47   | 6 1 3 | 47   5  8  |
+------------+-------+------------+
| 2  57 9    | 4 3 8 | 57   1  6  |
| 8  1  3    | 7 6 5 | 2    4  9  |
| 67 4  567  | 2 9 1 | 357  8  37 |
+------------+-------+------------+

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



Joined: 12 Feb 2006
Posts: 5165
Location: Rochester, NY, USA

PostPosted: Wed Jul 04, 2007 3:54 pm    Post subject: Re: Stuck Again Reply with quote

Earl wrote:
I can solve this with a forcing chain to a contradiction, which is almost trial and error. Anyone see a "logical" step?

Thanks

Earl

Code:

+------------+-------+------------+
| 16 9  168  | 3 5 7 | 68   2  4  |
| 4  3  2    | 1 8 6 | 9    7  5  |
| 5  67 78   | 9 4 2 | 38   36 1  |
+------------+-------+------------+
| 3  8  16   | 5 7 4 | 16   9  2  |
| 17 56 1457 | 8 2 9 | 1347 36 37 |
| 9  2  47   | 6 1 3 | 47   5  8  |
+------------+-------+------------+
| 2  57 9    | 4 3 8 | 57   1  6  |
| 8  1  3    | 7 6 5 | 2    4  9  |
| 67 4  567  | 2 9 1 | 357  8  37 |
+------------+-------+------------+

Play this puzzle online at the Daily Sudoku site


There is a Type 4 rectangle on 47 in boxes 4 and 6 which I don't know if it does any good. But there's an XY-Wing 17-16-67 which will accomplish something, but I don't know if it breaks the puzzle.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Wed Jul 04, 2007 7:50 pm    Post subject: Reply with quote

There is a W-Wing on 16 in Boxes 1 and 4.

Or, there is an XY-Chain with pincers at R4C7 and R5C1 that eliminates <1> from R5C7.
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Wed Jul 04, 2007 8:36 pm    Post subject: Reply with quote

There's also an X-wing/swordfish that removes >7> from r9c3, after which the XY-wing that Marty mentioned solves that same cell.
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Mogulmeister



Joined: 03 May 2007
Posts: 695

PostPosted: Wed Jul 04, 2007 11:47 pm    Post subject: Reply with quote

Picking up on Tracy's x-wing on 7's that removes the 7 from r9c3 (and a bunch of other 7's) This leaves a Y wing at r3c2 r7c2 r9c3 , (67-57-56)

............which knocks out the 6 at r1c3.

Another Y wing straight afterwards at r1c37 and r4c3 chops out yet another 6 and the puzzle is toast.
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