Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
Figure 16.4 Developing the Reversi game
Evaluating the computer’s best move
The evaluation function for the computer’s best move is the most complex part of the game to code
efficiently. The aim of the function is to derive the computer’s best move based on a look-ahead
of two moves. Because we do not want to affect the display we first copy the on-screen board into
a one-dimensional array called ‘board’. This array starts in the top left corner and scans the board
one row at a time; index 8 is therefore row 1 column 0.
After storing the board position in a format that is easily readable by the computer we then
process every square of the board looking for a legal move. The function used is ‘computerScore’;
this function returns −1 if the position is an illegal move and a score for the computer if the square
is a legal move. We will look a little later at how this score is derived. If the move is legal then
we use the position following this move that is stored in the single dimension array ‘cBoard’ in a
further function ‘playerScore’; the purpose of this function is to calculate the player’s best score
from the board position stored in the array ‘cBoard’. Then we subtract the player’s best score from
the computer’s best score and work out which move will give the computer the best advantage.
Finally, having discovered the best move on the basis of this simple algorithm, we calculate the
row and column that the move implies. Because the arrays are single dimensional to map to row
and column we use the code snippet:
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row = int(best/8);
col = best % 8;