Take four coins of the same size and make a
square as shown in the far left square in the illustration; two coins
- heads up in the top row, and the other two - tails up in the bottom
The object is to make another square with two coins heads up on one
diagonal and with two coins tails up on the other - as shown in the
right square in the illustration.
This should be performed in the shortest possible number of moves.
A move consists of sliding a pair of the two adjoining coins to a new
place. You have to slide the coins only orthogonally; it means that
you are not allowed to rotate the pair of coins while you move it. The
final square not necessarily needs to be formed exactly at the same
spot as the start square was.