stuck on USA Today 13 Jan 06

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stuck on USA Today 13 Jan 06

Postby retired_engineer » Sun Jan 29, 2006 11:29 pm

I would like some to explain the next step for me. I use the Simple Sudoku program and the Hint tells me about an X-Y Wing eliminating (I think) the 2 in R5, C9. XY Wing isn't discussed in the Help topics.

Thanks in advance:

*-----------*
|..1|.2.|.53|
|.4.|5.1|..6|
|.25|7..|..1|
|---+---+---|
|..6|.8.|...|
|..3|.1.|9..|
|...|.4.|5..|
|---+---+---|
|5.4|..2|.7.|
|8.7|.53|.4.|
|9.2|.7.|1..|
*-----------*


*-----------*
|..1|.2.|.53|
|.4.|5.1|..6|
|.25|7..|..1|
|---+---+---|
|..6|.8.|3..|
|..3|.1.|9..|
|...|34.|5..|
|---+---+---|
|534|1.2|.7.|
|817|.53|.4.|
|962|.7.|135|
*-----------*


*-----------------------------------------------------------*
| 67 89 1 | 48 2 4689 | 478 5 3 |
| 37 4 89 | 5 39 1 | 278 289 6 |
| 36 2 5 | 7 369 4689 | 48 89 1 |
|-------------------+-------------------+-------------------|
| 124 57 6 | 29 8 579 | 3 12 247 |
| 24 578 3 | 26 1 567 | 9 268 2478 |
| 12 789 89 | 3 4 67 | 5 1268 278 |
|-------------------+-------------------+-------------------|
| 5 3 4 | 1 69 2 | 68 7 89 |
| 8 1 7 | 69 5 3 | 26 4 29 |
| 9 6 2 | 48 7 48 | 1 3 5 |
*-----------------------------------------------------------*

P.S. Not sure why the 1st two grids above were pasted in from my 'copy/paste' of the puzzle, but I'll leave them here in case there is something of value.
retired_engineer
 
Posts: 4
Joined: 29 January 2006

Postby tarek » Mon Jan 30, 2006 1:39 am

The XY wing is as follows:
Code: Select all
*--------------------------------------------------------*
| 67    89    1    | 48    2     4689 | 478   5     3    |
| 37    4     89   | 5     39    1    | 278   289   6    |
| 36    2     5    | 7     369   4689 | 48    89    1    |
|------------------+------------------+------------------|
| 124   57    6    | 29    8     579  | 3     12    247  |
| 24    578   3    | 26    1     567  | 9     268   2478 |
| 12    789   89   | 3     4     67   | 5     1268  278  |
|------------------+------------------+------------------|
| 5     3     4    | 1     69    2    | 68    7     89   |
| 8     1     7    | 69    5     3    | 26    4     29   |
| 9     6     2    | 48    7     48   | 1     3     5    |
*--------------------------------------------------------*
Eliminating 2 From r5c9 (9 & 6 in r8c4 form an XY wing with 2 in r8c9 & r5c4)

However this doesn't solve the puzzle. Advanced techniques are needed.

Tarek
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Postby TKiel » Mon Jan 30, 2006 2:23 am

Retired Engineer,

To answer your ps: The first grid is the layout of initial clues, the second is the layout of solved cells at the time you cut and pasted, and the third is the second grid plus the candidates for the unsolved cells.
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Posts: 209
Joined: 05 January 2006

Postby retired_engineer » Mon Jan 30, 2006 5:19 am

Tarek:
Thanks, I think I've got XY Wing now. I see the logic. Can't believe USA Today Difficulty Rating of 5 stars has gotten so advanced. Been a while since I did a USA Today 5 star, but have always been able to figure them out witout needing advanced techniques.

TKiel:
Thanks for the info.
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Joined: 29 January 2006


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