def _min(self, board: Board) -> (float, int):
"""
Evaluate the board position `board` from the Minimizing player's point of view.
:param board: The board position to evaluate
:return: Tuple of (Best Result, Best Move in this situation). Returns -1 for best move if the game has already
finished
"""
#
# First we check if we have seen this board position before, and if yes just return the cached value
#
board_hash = board.hash_value()
if board_hash in self.cache:
return self.cache[board_hash]
#
# Init the min value as well as action. Min value is set to DRAW as this value will pass through in case
# of a draw
#
min_value = self.DRAW_VALUE
action = -1
#
# If the game has already finished we return. Otherwise we look at possible continuations
#
winner = board.who_won()
if winner == self.side:
min_value = self.WIN_VALUE
action = -1
elif winner == board.other_side(self.side):
min_value = self.LOSS_VALUE
action = -1
else:
for index in [
i for i, e in enumerate(board.state)
if board.state[i] == EMPTY
]:
b = Board(board.state)
b.move(index, board.other_side(self.side))
res, _ = self._max(b)
if res < min_value or action == -1:
min_value = res
action = index
# Shortcut: Can't get better than that, so abort here and return this move
if min_value == self.LOSS_VALUE:
self.cache[board_hash] = (min_value, action)
return min_value, action
self.cache[board_hash] = (min_value, action)
return min_value, action
def _min(self, board: Board) -> int:
"""
Evaluate the board position `board` from the Minimizing player's point of view.
:param board: The board position to evaluate
:return: returns the best Move in this situation. Returns -1 for best move if the game has already
finished
"""
#
# First we check if we have seen this board position before, and if yes just return a random choice
# from the cached values
#
board_hash = board.hash_value()
if board_hash in self.cache:
return random.choice(self.cache[board_hash])
#
# If the game has already finished we return. Otherwise we look at possible continuations
#
winner = board.who_won()
if winner == self.side:
best_moves = {(self.WIN_VALUE, -1)}
elif winner == board.other_side(self.side):
best_moves = {(self.LOSS_VALUE, -1)}
else:
#
# Init the min value as well as action. Min value is set to DRAW as this value will pass through in case
# of a draw
#
min_value = self.DRAW_VALUE
action = -1
best_moves = {(min_value, action)}
for index in [
i for i, e in enumerate(board.state)
if board.state[i] == EMPTY
]:
b = Board(board.state)
b.move(index, board.other_side(self.side))
res, _ = self._max(b)
if res < min_value or action == -1:
min_value = res
action = index
best_moves = {(min_value, action)}
elif res == min_value:
action = index
best_moves.add((min_value, action))
best_moves = tuple(best_moves)
self.cache[board_hash] = best_moves
return random.choice(best_moves)