## Coin Flip

In a row of four squares, place a penny, nickel, dime, quarter -
from left to right. The object is to reverse their order - that is,
to get them in the sequence quarter, dime, nickel, penny - in the
fewest possible turns. In each turn, move a coin one square to the
left or right. You may move a coin only into an empty square or onto
an adjacent coin of higher value (e.g., a penny can move onto a
nickel, but not vice versa.) Only the top coin of a stack may move.
What is the smallest number of turns necessary to effect the switch?
Source: Will Shortz, Games Magazine, August 1992.
Used as Ken's POTD 9/6/94.

Solution

Mail to Ken