The diagram shows a restricted chess board with three black knights and three white knights. Your goal is to move the pieces so that the same squares are occupied but the colors are reversed. Your first move must use a black piece.

Pieces may move only as a normal chess knight, from one corner of a 2×3 rectangle to the opposite corner. No more than one piece may occupy a single square at a time. No piece may move onto a darkened square. No other rules of chess apply.

One turn is a sequence of moves made by a single piece. Find a solution with the minimum number of turns.

This problem gives me a Rubiks cube feeling.  I mean that maybe subroutines should be found. 
The following sets knight b1 at d5 and d5 at b1.
I am pretty sure (Though not tested) that, with a 90 degree clockwise turn of the routine, it will also solve e2 and a4.  I'll  test it when (if ever) I have an idea to also solve d2 and d4.

b1 to c3
d2 b1
e2 d4
c3 e2
d5 c3
b4 d5
a4 b2
c3 a4
e2 c3
d4 e2
d5 b4
c3 d5
a4 c3
b2 a4
b1 d2
c3 b1

Posted by Hugo on 2004-12-10 20:39:05