The New Sudoku Players' Forum

[Dottor Zero]

Being a beginner I am using Simple Sudoku for it's great and instructive hint feature which confused me a little. I thought I understood the X-Wing method until the software told me that I should eliminate the 8 at r9c7 because of X-Wing. Could someone please explain?

Code: Select all

 *--------------------------------------------------*
 | 9    24   24   | 6    8    7    | 5    3    1    |
 | 1    3    8    | 5    2    9    | 7    6    4    |
 | 7    6    5    | 4    3    1    | 2    9    8    |
 |----------------+----------------+----------------|
 |*36   48   467  | 1    9    5    |*38   2    67   |
 | 25   28   1    | 3    7    6    | 4    58   9    |
 | 35   9    67   | 8    4    2    | 13   15   67   |
 |----------------+----------------+----------------|
 | 4    5    26   | 29   1    8    | 69   7    3    |
 | 28   7    3    | 29   6    4    | 189  18   5    |
 |*68   1    9    | 7    5    3    |-68   4    2    |
 *--------------------------------------------------*


[udosuk]

The program says XY-Wing not X-Wing. Read carefully.

[Dottor Zero]

Oops!

It was obviously much too late in the night for me...

[underquark]

Simple Sudoku is great but it doesn't do URs so misses out on the Unique Rectangle in R46C39:

Code: Select all

 *--------------------------------------------------*
 | 9    24   24   | 6    8    7    | 5    3    1    |
 | 1    3    8    | 5    2    9    | 7    6    4    |
 | 7    6    5    | 4    3    1    | 2    9    8    |
 |----------------+----------------+----------------|
 | 36   48  4-6-7 | 1    9    5    | 38   2   *67   |
 | 25   28   1    | 3    7    6    | 4    58   9    |
 | 35   9   *67   | 8    4    2    | 13   15  *67   |
 |----------------+----------------+----------------|
 | 4    5    26   | 29   1    8    | 69   7    3    |
 | 28   7    3    | 29   6    4    | 189  18   5    |
 | 68   1    9    | 7    5    3    | 68   4    2    |
 *--------------------------------------------------*


Way easier to spot (IMHO) than XY-wings. See the very in-depth descriptions of URs in this forum but, basically, you can't have 67 in each of four cells at the corners of a rectangle as this would lead to a possibility of more than one solution; the 4, in this case, has to be a winner.

[Dottor Zero]

Yes, I also noticed it later. Thanks guys.