Medusa+Forward Logic solves 870 of top870

Bob Hanson

OK, here you go:

Sudoku Assistant

http://www.stolaf.edu/people/hansonr/sudoku

just solved all 870 of these with nothing more than simple human strategies, strong chains, weak links, and simple logic.

The first 509 I solved using "proof"-based reverse logic
The next 324 I solved using "disproof"-based forward logic
The next 37 I solved using "proof"-based reverse logic

total solved: 870

The forward variety amounts to

"Hypothesis: This cell cannot be eliminated"
followed by proof that it must be eliminated or "I don't know"

The reverse variety amounts to

"Hypothesis: This cell can be eliminated"
followed by proof that this must be the case or "I don't know"
_________________
Bob Hanson
Professor of Chemistry
St. Olaf College
Northfield, MN
http://www.stolaf.edu/people/hansonr

rubylips

Bob Hanson · Posted: Sat Nov 05, 2005 8:07 pm Post subject:

Sure. The way to get this is as follows:

1) fire up http://www.stolaf.edu/people/hansonr/sudoku

2) click on "Number Block Input"

3) If you have the puzzle in a simple format

020304050
1030........

for example -- just about anything can be read ---

just clip in there.

4) If you don't have it, click on "your own file", which
is preset for top870. Just click OK. The website will load all 870 into
a selection box. (A neat trick I recently learned.)

5) Find the puzzle you want and click "load selected" or "standard view" or "solve"

--Oh, wait -- that LOOONG link I provided -- click on that -- it should pop right up. Forget Steps 2-5.

Anytime you want to return to the starting point, click "Start Over". This clears the puzzle to its initial state, with the givens in place. (Don't click Reset -- that completely clears the puzzle.)

What I typically do is turn OFF Medusa and Solve. This will, of course, get stuck. That's OK. Then I turn it ON and Step through the next step or two to see what made it get stuck. The "[snapshot]" link on the right is kind of interesting. It loads a new page with the puzzle at that exact state of solution so you can play with it -- just after checking for singles but BEFORE the step of interest. That's the looong link I provided.

To visualize the chains, you can click on one of the "strong chain" links or you can go to 3D view and see them all in 3D.

If you want the detailed listing of the chain and weak node information, click the "detail" option before you Step. There's a lot that comes out -- all the chain lists, the weak links and corner lists, a table that maps the connectivity of the chains, and a list of all the weak nodes. It's mostly readable, but there's a LOT there.

Realize that the chain/node information is all recreated for each step in the process. So it's different each step.

It's nice to have the "standard view" right in front of you when you look at the table, because then you can click on a strong chain link (as in <a>3</a>) and see the highlighted cells of the chain. The (1) nodes are dark blue marks; the (0) nodes are light blue.

Tell me if this doesn't work for you.
_________________
Bob Hanson
Professor of Chemistry
St. Olaf College
Northfield, MN
http://www.stolaf.edu/people/hansonr