The New Sudoku Players' Forum

[speter]

G'Day Folks,

I'm starting to code y-wing strategy into my sudoku program.

The 'classic' representation of y-wing (from http://www.sudokuwiki.org/Y_Wing_Strategy) is:

Code: Select all

  . .  . | . .  .
  . AB . | . BC .
  . .  . | . .  .
  -------+--------
  . .  . | . .  .
  . AC . | . C  .

where:
  AB = pivot
  BC & AC = pincers
  C can be discarded.


My question is, is it (also) possible to have:

Code: Select all

  . .  . | . .  . | . .  .
  . AB . | . BC . | . BD .
  . .  . | . .  . | . .  .
  -------+--------+--------
  . .  . | . .  . | . .  .
  . AC . | . C  . | . .  .
  . .  . | . .  . | . .  .
  -------+--------+--------
  . .  . | . .  . | . .  .
  . AD . | . .  . | . D  .

where:
  AB = pivot
  BC & AC = pincers
  C can be discarded.
and
  BD & AD = pincers
  D can be discarded.


In other words, can y-wing's pivots be "used" multiple times, using the same (where C = D) or different (where C != D) discard candidates?

[JasonLion]

Welcome to the Sudoku Players Forum!

Yes, of course. Nothing about a Y-Wing "uses up" the pivot, so you are free to use the pivot in another Y-Wing. More generally, as long as the criteria for a Y-Wing are met, you can use it. It doesn't matter what other patterns are present at the time or what the history of your deductions up to that point is (as long as you haven't made any mistakes).

[speter]

Thanks for the welcome and the answer.