class AlphaBetaTree(GameTree):
def __init__(self, data = None):
GameTree.__init__(self, data)
def evaluate(self, evaluator):
return self.alphaBeta(evaluator)
def alphaBeta(self, evaluator, alpha = -Decimal('infinity'), beta = Decimal('infinity')):
if (self.hasChildren()):
for child in self.children():
alpha = max(alpha, - child.alphaBeta(OppositeTo(evaluator), -beta, -alpha))
if (beta <= alpha):
break
return alpha
return evaluator.value(self.data())
if __name__ == '__main__':
import Evaluator
assert AlphaBetaTree() != None
identity = Evaluator.IdentityEvaluator()
assert AlphaBetaTree(0).evaluate(identity) == 0
assert AlphaBetaTree(1).evaluate(identity) == 1
root = GameTree(0)
root.addChild(GameTree(0).addChild(GameTree(1)).addChild(GameTree(2)))
root.addChild(GameTree(0).addChild(GameTree(-1)).addChild(GameTree(-3)))
assert root.evaluate(identity) == 1
