Hidden Doubles, Triples, and Quads are never used

rantinori

This is my first post and like so many of you in this forum I have become fascinated with the techniques required to programmatically solve a Sudoku puzzle.

I have discovered that by first finding all EXPOSED pairs, triples, and quads and then using these to eliminate candidates in other cells all HIDDEN pairs, triples, and quads are eliminated. If this observation is true for all possible Sudoku puzzles, then no programmed solution would need to consider these Hidden conditions.

Can anyone confirm this observation?

Ruud · Site Admin

Hi,

You are not the only one having made that discovery.

Please follow this link:

http://www.setbb.com/sudoku/viewtopic.php?t=273&mforum=sudoku

And read all replies to it. Your statement is correct, but for performance reasons, you should not abandon the search for hidden subsets.

Ruud.
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gonzo · Posted: Sun Jan 29, 2006 1:39 pm Post subject:

No, I think you're wrong there.

I made my solver so you can choose each step individually. I can go through the exposed, the program automatically solves and then updates in all other cells, but after running through all the exposed, you can still find hidden.

An interesting thing - when I wrote my code to search for hidden, I realized that it took care of the exposed as well, so that may be a route to solving you might want to persue, have your code search for these pairs, triples and quads regardless of what other candidates may exist in the cells.

rantinori · Posted: Sun Jan 29, 2006 4:34 pm Post subject:

Ruud, Thanks for your response. You've given me a lot to read and digest. I coded my solution in VB6 and find that performance is not an issue. The process to discover cell values by searching for these various conditions is almost instantaneous.

I posted the observation because there are so many people on this forum writing code and discussing coding approaches to solutions that I believe it would be beneficial to them to eliminate one more sets of algorithms to code and debug.

Gonzo, Thanks you. Could you post a puzzle that exhibits the conditions you describe? I'd like to test it with my program.