def minimax(tree: GameStateTree, num_rounds: int, maximizing_player: Player) -> Tuple[int, Action]:
"""
Called recursively on various nodes of the GameStateTree to determine the maximum move for the maximizing player
and the minimizing move for any player that is not the maximizing player.
:param tree: The game state tree that will be examined to determine the optimal moves.
:param num_rounds: The number of rounds each player will play within the decision algorithm
:param maximizing_player: The player that is being maximized, all other players will attempt to minimize this player.
:return: The Tuple(optimal_score, optimal_action) that will take place in this round of the minimax algorithm.
"""
if num_rounds == 0 and tree.state.current_player.color == maximizing_player.color:
return tree.state.current_player.score, tree.previous_action
elif tree.state.phase == GameStatePhase.OVER and tree.state.current_player.color == maximizing_player.color:
return tree.state.current_player.score, tree.previous_action
# if we reach the end and it is the maximizing players turn return the maximizing players score
elif tree.state.phase == GameStatePhase.OVER and tree.state.current_player.color != maximizing_player.color:
return -inf, None
# if we reach the end and it is not the maximizing players turn return the -inf so
# the next node up the chain will be greater than it
elif tree.state.current_player.color == maximizing_player.color: # maximize this player
children = [child for child in tree.get_children()]
return GenericStrategyComponent.handle_maximum(
children=children, num_rounds=num_rounds, maximizing_player=maximizing_player)
elif tree.state.current_player.color != maximizing_player.color:
# minimize the maximizing player for all other player
children = [child for child in tree.get_children()]
return GenericStrategyComponent.handle_minimum(
children=children, num_rounds=num_rounds, maximizing_player=maximizing_player)
def test_create_choose_action_recursive_case_is_maximizing_twice(self):
"""
In a recursive case where 1 round is played and the
all leave nodes are the maximizing players, the minimum of
these leave nodes is return.
"""
state, *_ = self.setup()
production_tree = GameStateTree(state, previous_action=None)
expected = Action(
player_color=production_tree.state.current_player.color,
start=Coordinate(0, 0),
end=Coordinate(1, 0))
children = [child for child in production_tree.get_children()]
for idx, child in enumerate(children):
second_players_children = [
second_players_child
for second_players_child in child.get_children()
]
for jdx, second_players_child in enumerate(
second_players_children):
if jdx == 1 and idx == 1:
score = 0
child.previous_action = expected
else:
score = 10
modified_player = Player.from_dict({
**second_players_child.state.current_player._asdict(),
**{
'score': score
}
})
second_players_child.state.current_player = modified_player
second_players_child.get_children = MagicMock(return_value=[])
second_players_child.state.check_any_player_can_move = MagicMock(
return_value=False)
production_tree.get_children = MagicMock(return_value=children)
actual = GenericStrategyComponent.choose_action(tree=production_tree,
num_turns=2)
self.assertEqual(expected, actual)
def test_create_choose_action_recursive_case_is_maximizing_once(self):
"""
In a scenario where all the children of the maximizing player
are leaves - aka end-games - than a tie-breaker decides which
action to take.
"""
state, *_ = self.setup()
production_tree = GameStateTree(state, previous_action=None)
expected = Action(
player_color=production_tree.state.current_player.color,
start=Coordinate(0, 0),
end=Coordinate(1, 0))
children = [child for child in production_tree.get_children()]
for idx, child in enumerate(children):
if idx == 1:
child.previous_action = expected
child.get_children = MagicMock(return_value=[])
production_tree.get_children = MagicMock(return_value=children)
actual = GenericStrategyComponent.choose_action(tree=production_tree,
num_turns=2)
self.assertEqual(expected, actual)
def test_create_choose_action_base_case_0_turns(self):
"""
If the player has 0 turns and it is the currents player turn,
then the previous action is return.
"""
state, *_ = self.setup()
production_tree = GameStateTree(state, previous_action=None)
production_tree.get_children = MagicMock(return_value=None)
expected = Action(
player_color=production_tree.state.current_player.color,
start=Coordinate(0, 0),
end=Coordinate(1, 0))
production_tree.previous_action = expected
actual = GenericStrategyComponent.choose_action(tree=production_tree,
num_turns=0)
self.assertEqual(expected, actual)
def test_create_choose_action_base_case_no_children_for_non_maximizing_player(
self):
"""
If the player has turns > 0 but has no children - end-game - and this is not
the maximizing player, then we return None.
"""
state, *_ = self.setup()
production_tree = GameStateTree(state, previous_action=None)
production_tree.get_children = MagicMock(return_value=[])
production_tree.previous_action = Action(
player_color=production_tree.state.current_player.color,
start=Coordinate(0, 0),
end=Coordinate(1, 0))
expected = None
_, actual = GenericStrategyComponent.minimax(tree=production_tree,
num_rounds=2,
maximizing_player=Player(
"white", 0, 0, []))
self.assertEqual(expected, actual)