I’m not sure what was different between your two posts, but I’ll respond to this one.
My definition of a pruning opportunity is (1) all moves can be ignored if a layout has been reached before, or (2) all moves but one can be ignored from a layout if it can be proven that the one move cannot possibly prevent a solution, or (3) a particular move can be ignored if it can be proven (with little or no look ahead) that it cannot possibly lead to a solution. Have I missed anything?
In your scenario, we have 2 choices at move 10: (10. 61) and (10. 15). While I would always try (10. 15) first, both moves are irreversible, and I don’t see how you could prove that (10. 61) could not possibly be necessary to a solution (without some kind of look ahead). Neither subsequent sequence of moves leads to a repeated layout (until you come to the last move, at which point there are no more moves possible).
Somehow, I get the feeling you don’t see it as being this simple, so I must be missing something.
-Gary
From: dannyjones183
Sent: Monday, October 08, 2012 12:26 PM
To: fc-solve-discuss_at_yahoogroups.com
Subject: Missed Pruning Opportunity ?
First off, it really sucks that a post must be deleted in order to edit it!!!
Below is an unsolveable puzzle and two (partial) move sequences for it. The move sequences result in identical layouts, and their first nine moves are identical. (Freecells are considered equivalent if their combined contents are the same in two layouts.)
Did I miss a pruning opportunity in the last five moves of the first sequence? All I see is an extraneous 3C move, but it isn't obvious since the 2H must be moved on top of it in order for the 9S move to occur.
#88445005 Attempt: 1 NumFcs=4 (Hrn Super)
7a 7b 7c 7d b7 5b d7 17 6d 15 65 a6 5a 5h
9S 9H 5S 8C 9H 7H 8C 7D 5D 3C 2H 9S 2H 3C
| | | | | | | | |
7a 7b 7c 7d b7 5b d7 17 6d 61 a6 1a 1h
9S 9H 5S 8C 9H 7H 8C 7D 5D 2H 9S 2H 3C
Received on Mon Oct 08 2012 - 13:31:35 IST