Game Development Reference
judgment on an indeterminate game. Heuristics provide guidance to the eva-
luation function in otherwise ambiguous circumstances. Pruning methods often
need help as well. What moves can safely be ignored? What moves are the most
promising? Heuristics provide guidance to pruning as well as to evaluation. Note
that risky, high-payoff moves illustrate differences between the needs of eva-
luation and the needs of pruning. Risky moves evaluate poorly because of the
risk. If we prune them, we will not exploit the ones with a high payoff that
follows. In short, heuristics are very important to game AI. Tic-Tac-Toe is too
small for good heuristics, but Fox and Hounds is not. A brief description of Fox
and Hounds is in order.
Fox and Hounds is played on the dark squares of a standard checkerboard. The
fox moves like a king in checkers. The hounds move like regular checkers; they
cannot move backward. There is no jumping and no capturing. Once a hound
reaches the far end of the board, it can no longer move. The goal of the hounds is
to pin the fox so that it cannot move. The goal of the fox is to get past the hounds.
The fox moves first. The game starts with four hounds at one end of the board
and the fox at the other, as shown in Figure 6.2.
Opening board for Fox and Hounds.