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October 8 - Very Hard

 
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dshannaaz



Joined: 30 Jul 2006
Posts: 2

PostPosted: Thu Oct 12, 2006 1:43 am    Post subject: October 8 - Very Hard Reply with quote

I usually struggle with the "hard" and "very hard" daily sudokus. I have also read that they are/will be getting even harder. Thus, I was surprised to speed through the October 8 "very hard" entry with nothing much more difficult than a naked pair. I am fairly certain I am not getting that much better and thus (alas) I wonder if it was mislabeled.
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TKiel



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

PostPosted: Thu Oct 12, 2006 10:24 pm    Post subject: Reply with quote

Up to this point nothing is needed but singles and locked candidates (b/b interaction):
Code:

 *-----------------------------------------------------------*
 | 4     278   2578  | 35    6     25    | 59    379   1     |
 | 9     12    125   | 4     235   7     | 6     8     35    |
 | 57    3     6     | 8     1     9     | 4     27    25    |
 |-------------------+-------------------+-------------------|
 | 6     17    3     | 157   57    8     | 2     4     9     |
 | 8     5     9     | 2     4     6     | 3     1     7     |
 | 2     4     17    | 17    9     3     | 8     5     6     |
 |-------------------+-------------------+-------------------|
 | 35    28    4     | 9     235   1     | 7     6     2358  |
 | 357   9     2578  | 6     2357  4     | 1     23    2358  |
 | 1     6     257   | 357   8     25    | 59    239   4     |
 *-----------------------------------------------------------*

after which Simple Sudoku says that an X-wing is the simplest next step, and it solves the puzzle. Actually there are three X-wings at this point, two of which solve the puzzle. This fits with the site definition of a 'Very Hard' puzzle. Where did you find the naked pair?
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dshannaaz



Joined: 30 Jul 2006
Posts: 2

PostPosted: Sat Oct 14, 2006 12:17 am    Post subject: No X-wings Reply with quote

I am not sure if I can recreate the logic. I do know that I did NOT use X-wings. In "very hard" sudokus there is usually a "sticking point" somewhere around move #12. I just didn't find one in this puzzle.

My first 20 moves were as follows:

R8C7; R2C1; R6C5; R4C7; R5C5;
R9C2; R4C1; R6C7; R5C9; R5C1;
R6C8; R6C9; R3C7; R2C7; R1C8;
R3C8; R9C7; R1C7; R3C9; R2C9.
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TKiel



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

PostPosted: Thu Oct 19, 2006 1:24 am    Post subject: Reply with quote

These all seem to be naked or hidden singles, up to r3c7 which seemed to be the result of the (2,5,7) naked triple in row 3. That turned r2c7 into a single, but I couldn't figure out how or what you placed in r1c8 at this time.
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