questions regarding the use of A* with the 15-square puzzle

Question

I\'m trying to build an A* solver for a 15-square puzzle.

The goal is to re-arrange the tiles so that they appear in their natural positions. You can only sli

Answer 1

What are you using for test data? If it's random, you will not be able to solve the puzzle about half the time. It is not possible to switch two tiles while keeping the rest in the same position, and so if you reach what is almost the end position but has two tiles interchanged, you can't possibly get it into the desired position, and no search algorithm can possibly terminate successfully.

In the 19th Century, American puzzlemaster Sam Loyd sold these toys with the 15 and 14 reversed, and offered a big prize for anybody who could demonstrate a solution switching the tiles (presumably other than the one I've got, a small screwdriver). In today's legal climate, I don't know if he'd have dared.

One possibility would be to try to get it into either the correct configuration or the 15-14 configuration.