Let's begin this lesson with a look at
a common single player game called eight
puzzle.
Eight puzzle is a sliding tile game.
The game board is a three by three square,
with number tiles in all but one of the
cells.
The state of the game is modified by
sliding
number tiles into the empty space from
adjacent cells.
Thus moving the empty space to a new
location.
there are four possible moves in, at most
four possible moves.
Moving empty space up, down, left or
right.
Obviously not all these moves are possible
on all states.
States shown on the left and right here
illustrate
the possible moves from the state shown in
the center.
The tile could be moved down.
The emp, I'm sorry, the empty cell can be
moved
down, the empty cell can be moved to the
right.
The ultimate objective of the game is to
place the tiles in order,
and position the empty square in the lower
right cell, as shown here.
the game terminates after 8 moves or when
all of
the tiles are in their right positions,
whichever comes first.
In some versions of the game, partial
credit
is given for states that approximate the
ultimate goal.
With ten points being allocated for each
numbered tile in the correct position,
and 20 points being allocated for having
the empty tile in the correct position.
For example, the first state shown here is
worth 40 points, since
four of the cells, the ones colored green
are in their correct positions.
And the second stage on here is worth a
hundred points since all of the tiles
are in their correct positions, and the
empty
cell is in the lower right hand corner.
Now as with other games, it is possible to
describe eight puzzle in GDL.
Here are the rules for three puzzle, its a
version of
eight puzzle in a two by two board without
partial credit.
Rules for eight puzzle with partial credit
are, are very much the same,
except they're a little more verbose, and
wouldn't easily fit on a page.
We won't go through the details of either
rule set in
this lesson, but it may be worth your
while to pause and
look over the rules and be sure you
understand them.
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