an EXTREMELY EASY Sudoku I couldn´t solve...

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an EXTREMELY EASY Sudoku I couldn´t solve...

Postby NoClue » Tue Apr 12, 2011 11:44 pm

Hi, all,

I couldn´t solve another EXTREMELY (!!!!!) EASY Sudoku. (difficulty very hard - # 649388):

Code: Select all
+-----+-----+-----+
|3 1 .|7 . .|6 2 .|
|7 . 5|. 3 .|8 . .|
|. 8 .|. . .|. . .|
+-----+-----+-----+
|. . 9|. . 7|. . .|
|8 . .|9 . 6|. . 3|
|. . .|5 . .|4 . .|
+-----+-----+-----+
|. . .|. . .|. 4 .|
|. . 3|. 9 .|7 . 5|
|. 9 6|. . 5|. 3 8|
+-----+-----+-----+


This Sudoku has 28 clues, I could hardly find ANY hidden singles (only 27) - and I had to pencilmark 26 (!!!!!) cells:

Code: Select all
+----------+-----------+---------+
|3.. 1... 4|7.. 5.. 8..|6.. 2 9..|
|7.. 6... 5|2.. 3.. 9..|8.. 1 4..|
|9.. 8... 2|146 146 14.|3.. 5 7..|
+----------+-----------+---------+
|246 2345 9|134 124 7..|125 8 126|
|8.. 245. 1|9.. 24. 6..|25. 7 3..|
|26. 23.. 7|5.. 8.. 123|4.. 9 126|
+----------+-----------+---------+
|5.. 7... 8|136 126 123|9.. 4 12.|
|124 24.. 3|8.. 9.. 124|7.. 6 5..|
|124 9... 6|14. 7.. 5..|12. 3 8..|
+----------+-----------+---------+


I couldn´t see ANY logical steps, even though there were so many cells, I had to pencilmark.

Any hints and tipps will be appreciated. Thanks in advance
NoClue
 
Posts: 48
Joined: 01 April 2011

Re: an EXTREMELY EASY Sudoku I couldn´t solve...

Postby eleven » Wed Apr 13, 2011 12:43 pm

Maybe not your favorite technique ...
Code: Select all
+------------+-------------+-----------+
| 3   1   4  | 7   5   8   | 6   2  9  |
| 7   6   5  | 2   3   9   | 8   1  4  |
| 9   8   2  | .   .   14  | 3   5  7  |
+------------+-------------+-----------+
| #   .   9  | .   .   7   | .   8  #  |
| 8   .   1  | 9   24  6   | 25  7  3  |
| 26  23  7  | 5   8   .   | 4   9  #  |
+------------+-------------+-----------+
| 5   7   8  | .   .   .   | 9   4  12*|
| *   24  3  | 8   9   .   | 7   6  5  |
| *   9   6  | 14  7   5   | 12  3  8  |
+------------+-------------+-----------+

Possible deadly pattern (DP) 26 in r46c19. The 6 must be in 2 of the cells, so only a 2 can and must be outside in the rows/columns/boxes.
Looking at the columns you have the *-ed cells as possibilities for 2.
A 2 in r89c1 implies r8c2=4, and
r7c9=2->r9c7=1->r9c4=4
So one of r8c2 and r9c4 must be 4 => r9c4=4.

To finish, look if you can eliminate a 1 with grouped skyscraper (finned x-wing) or empty rectangle.
eleven
 
Posts: 1559
Joined: 10 February 2008

Re: an EXTREMELY EASY Sudoku I couldn´t solve...

Postby NoClue » Wed Apr 13, 2011 4:07 pm

Hi, eleven,

yes, you´re absolutely right - Deadly Pattern, Finned X-Wing and Grouped Skyscraper are really not my favorite techniques. Even though of this, thank you for your tips.
NoClue
 
Posts: 48
Joined: 01 April 2011


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