The New Sudoku Players' Forum

[bradles]

Hi Guys,

I don't know if images are allowed here but I have posted one. Apologies if they are not allowed.

My understanding of x-wings is fairly basic. I came across this weird looking x-wing suggestion in simple sudoku and couldn't understand its logic? Would someone be kind enough to explain how this one works?



Brad

[CathyW]

Images are OK as long as the file size isn't too big and wherever you're hosting it won't disappear and render your post meaningless!

What you have here is not an x-wing but an xy-wing. I can't explain it any better than Simes here or Angus on another post in these forums here

You can eliminate the 2 from r9c7. HTH

[vidarino]

It's not an X-Wing, it's an XY-Wing, which is a different beast altogether (despite the confusingly similar name).

It works like this; Consider the cell R8C7 (candidates 38). If that cell is 3, it will force the cell in R7C8 (candidates 23) to become 2. And if it's 8, it will put a 2 in the cell R3C7 (candidates 28).

So we don't know which one of the candidates 3 or 8 is correct, but no matter which it is, a 2 will be eliminated from R9C7 (yellow cell), since it can "see" both the possible resulting 2s.

Hope that made sense. If not, demand a better explanation.

Vidar

(Edit: or follow the links in CathyW's post above.)

[bradles]

Images are OK as long as the file size isn't too big and wherever you're hosting it won't disappear and render your post meaningless!

Good point. Next time I think I will post the image but also the code showing the grid in text form.

[Animator]

I don't know if images are allowed here but I have posted one. Apologies if they are not allowed.

As far as I know they are not dis-allowed but I personally am very much against it.
There are things for which it makes sense to use an image, but this is not one of them IMHO.

a) it's hosted at a server over which you have no control,
b) the image might disappear any minute (making all this useless)
c) the loading of the page now depends on yet another server...
d) if someone want to solve the grid in their favourite-solving tool then they need to re-type everything since they can't do a copy/paste. (which is a common source of errors)
(e) the image might be larger then one's screen resolution. It's possible to do that with text aswell but that's more unlikely. To view your image without needing to scroll you need a resolution of 1024x768. To view the text-version you need a resolution of 640x480 (which is the lowest I can check). )

The grid:

Code: Select all

3  48  1   | 24  5  7   | 9    6     28
2  7   9   | 6   1  8   | 35   4     35
6  48  5   | 24  3  9   | 28+  7     1
-----------+------------+----------------
1  6   4   | 58  2  3   | 7    9     58
9  35  7   | 58  6  4   | 1    2358  2358
8  35  2   | 7   9  1   | 6    35    4
-----------+------------+----------------
5  9   36  | 1   8  26  | 4    23+   7
4  2   38  | 9   7  5   | 38+  1     6
7  1   68  | 3   4  26  | 258- 258   9

[bradles]

Thanks animator. I'll post text from now on.

Brad