Here a little challenge I found in an old quiz book which I'd like to offer for diversion.

On a 3x4 chess board 3 black and white knights are positioned at opposite ends. 

XXX
...
...
OOO

[download]

What's the minimal number of moves to swap their positions?

Write a Perl program calculating (and proving) an optimal solution and printing all intermediary steps.

Like ... 

OOO 
.X.
...
XX.

[download]

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

Update

Please use <spoiler> tags when posting solutions :)

In reply to [code challenge] knights move by LanX

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