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Sept 30 V Hard

 
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
PostPosted: Wed Sep 30, 2009 7:50 am    Post subject: Sept 30 V Hard Reply with quote
if one wishes to be perverse then this can be "solved" on the second entry!
Quote:
Enter the 8 in r2c2. This gives 37 in boxes A and F. These form a W-wing acting on the 3s in col2- and eliminate the 7 in r1c1
. Job Done!
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arkietech



Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
PostPosted: Wed Sep 30, 2009 11:49 am    Post subject: Reply with quote
I used a:
Quote:
235 xy-wing
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
PostPosted: Wed Sep 30, 2009 2:34 pm    Post subject: Reply with quote
I also noted the move spotted by Dan, but only after seeing
Quote:
the xy-wing 2-35 as a short chain involving the same four cells: (3)r3c3 - (3=2)r5c2 - (2=5)r6c2 - (5=3)r1c2; r3c3<>3.

Ted
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nancyroa



Joined: 04 Oct 2009
Posts: 2
PostPosted: Sun Oct 04, 2009 4:18 pm    Post subject: Reply with quote
Could one of you draw out the logic more clearly? I have been working on this puzzle for 4 days - went back, read about w-wing, chains, etc - and still can't figure out how to do this one. ARGH!

Thanks for any help - Nancy
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
PostPosted: Sun Oct 04, 2009 8:11 pm    Post subject: the W-Wing solution Reply with quote
nancyroa wrote:
Could one of you draw out the logic more clearly? I have been working on this puzzle for 4 days - went back, read about w-wing, chains, etc - and still can't figure out how to do this one. ARGH!

Thanks for any help - Nancy

Code:

+-----------------+-------------------+--------------+
| 357  35   9     | 1378  13478  4678 | 4678 567 2   |
| 2    8    17    | 179   5      467  | 4679 679 3   |
| 4    6    37    | 2     3789   78   | 1    579 578 |
+-----------------+-------------------+--------------+
| 358  1    348   | 6     78     9    | 2    357 578 |
| 3589 7    238   | 158   128    258  | 3689 4   568 |
| 589  259  6     | 4     278    3    | 789  1   578 |
+-----------------+-------------------+--------------+
| 37   234  5     | 37    2347   1    | 367  8   9   |
| 1    239  2378  | 35789 6      2578 | 37   237 4   |
| 6    2349 23478 | 3789  234789 2478 | 5    237 17  |
+-----------------+-------------------+--------------+

Play this puzzle online at the Daily Sudoku site


The 8 in Box 1 is straghtforward and this gives the above grid.There is a 37 in box 1 and another in box 7 If both were 3 then col 2 will fail because there is no place for a 3. Therefore at least one of the 37s must be 7 so any cell that sees both 37s cannot be a 7 and that includes cells r8c3 and r9c3 that leaves only r7c1 as 7 , and from here solving the rest is easy!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun Oct 04, 2009 9:02 pm    Post subject: Re: the W-Wing solution Reply with quote
George Woods wrote:
nancyroa wrote:
Could one of you draw out the logic more clearly? I have been working on this puzzle for 4 days - went back, read about w-wing, chains, etc - and still can't figure out how to do this one. ARGH!

Thanks for any help - Nancy

Code:

+-----------------+-------------------+--------------+
| 357  35   9     | 1378  13478  4678 | 4678 567 2   |
| 2    8    17    | 179   5      467  | 4679 679 3   |
| 4    6    37    | 2     3789   78   | 1    579 578 |
+-----------------+-------------------+--------------+
| 358  1    348   | 6     78     9    | 2    357 578 |
| 3589 7    238   | 158   128    258  | 3689 4   568 |
| 589  259  6     | 4     278    3    | 789  1   578 |
+-----------------+-------------------+--------------+
| 37   234  5     | 37    2347   1    | 367  8   9   |
| 1    239  2378  | 35789 6      2578 | 37   237 4   |
| 6    2349 23478 | 3789  234789 2478 | 5    237 17  |
+-----------------+-------------------+--------------+

Play this puzzle online at the Daily Sudoku site


The 8 in Box 1 is straghtforward and this gives the above grid.There is a 37 in box 1 and another in box 7 If both were 3 then col 2 will fail because there is no place for a 3. Therefore at least one of the 37s must be 7 so any cell that sees both 37s cannot be a 7 and that includes cells r8c3 and r9c3 that leaves only r7c1 as 7 , and from here solving the rest is easy!


The above grid has a 37 pair in row 7. After making some eliminations therefrom, the XY-Wing mentioned earlier is exposed. The pivot of 25 is in r6c2 and the pincer cells of 23 and 35 are in r5c3 and r1c2, taking out the 3 from r3c3.

Code:

+-----------------+-------------------+-------------+
| 357  35   9     | 1378  13478  4678 | 478 567 2   |
| 2    8    17    | 179   5      467  | 479 679 3   |
| 4    6    37    | 2     3789   78   | 1   579 578 |
+-----------------+-------------------+-------------+
| 358  1    34    | 6     78     9    | 2   357 578 |
| 3589 7    23    | 158   128    258  | 389 4   568 |
| 589  25   6     | 4     278    3    | 789 1   578 |
+-----------------+-------------------+-------------+
| 37   24   5     | 37    24     1    | 6   8   9   |
| 1    239  2378  | 35789 6      2578 | 37  237 4   |
| 6    2349 23478 | 3789  234789 2478 | 5   237 1   |
+-----------------+-------------------+-------------+

Play this puzzle online at the Daily Sudoku site
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nancyroa



Joined: 04 Oct 2009
Posts: 2
PostPosted: Mon Oct 05, 2009 6:08 pm    Post subject: Thank you! Reply with quote
Thanks very much! - Nancy
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