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june 28 DB

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Jun 28, 2008 12:38 pm    Post subject: june 28 DB Reply with quote
The June 28 DB succumbs to a UR. If you don't use the UR, it takes coloring in 3, then 9, and finally an xy-chain, or myriad other solutions. Go UR !

Earl

Code:

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

Play this puzzle online at the Daily Sudoku site
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria
PostPosted: Sun Jun 29, 2008 9:37 am    Post subject: Re: june 28 DB Reply with quote
Earl wrote:
... myriad other solutions. Go UR !


After basics, when the 49 UR is beckoning so temptingly, there is a rather short xy-chain that completely solves the puzzle:

Code:

+--------------------------+--------------------------+--------------------------+
| 5       6       4        | 17      9       17       | 3       2       8        |
| 1       3       7        | 28      68      26       | 49      49      5        |
| 2       9       8        | 3       4       5        | 1       7       6        |
+--------------------------+--------------------------+--------------------------+
| 3489    248     1        | 6       5       249      | 49      349     7        |
| 49      7       5        | 129     3       1249     | 6       8       129      |
| 6       24      39       | 129     7       8        | 5       1349    1239     |
+--------------------------+--------------------------+--------------------------+
| 89      18      6        | 4       2       3        | 7       5       19       |
| 379     15      39       | 5789    68      679      | 2       1369    4        |
| 3479    45      2        | 579     1       679      | 8       369     39       |
+--------------------------+--------------------------+--------------------------+

Hint 1: look at boxes 4 and 7
Hint 2: 49 in r5c1 and 45 in r9c2 act as pincers, the group 89-18-15 supplies the missing link (effectively the same as a 95 cell in an xy-wing) and 4 is removed from r46c2 and r9c1...
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