Single player game
The objective is to eliminate as many balls as possible.
Each move consists of clicking on a filled square and then clicking
on an empty square with exactly one square in between, which must be
filled. The ball on the original square goes to the empty square and
the middle ball disappears. Diagonal moves are not allowed.
If you have managed to leave only a single ball remaining then try the
problem of leaving only a single ball on the center square.
Get the balls out of the edges as soon as possible.