def minimax(board,
depth,
player,
alpha=-np.inf,
beta=np.inf,
eval_func='pos_score',
king_version=False):
if depth == 0:
if eval_func == 'pos_score':
return pos_score_sum(board)
elif eval_func == 'mobi':
return mobility(board)
elif eval_func == 'pos_mobi':
return pos_plus_mobi(board)
elif eval_func == 'king_pos_score': # this is for King Othello
return king_pos_score_sum(board)
if not king_version:
game = Othello()
else:
game = KingOthello()
game.board = board
game.current_player = player
possible_moves = game.find_all_valid_moves()
if possible_moves:
if player == BLACK: # maximizing player
max_eval = -np.inf
for move in possible_moves:
game_copy = deepcopy(game)
game_copy.take_move(move[0], move[1])
eval = minimax(game_copy.board, depth - 1, opposite(player),
alpha, beta)
max_eval = max(max_eval, eval)
alpha = max(alpha, eval)
if beta <= alpha:
break
return max_eval
else: # WHITE, minimizing player
min_eval = np.inf
for move in possible_moves:
game_copy = deepcopy(game)
game_copy.take_move(move[0], move[1])
eval = minimax(game_copy.board, depth - 1, opposite(player),
alpha, beta)
min_eval = min(min_eval, eval)
beta = min(beta, eval)
if beta <= alpha:
break
return min_eval
else: # no possible move for current player
game.switch_turn()
possible_moves = game.find_all_valid_moves(
) # check whether opponent has moves
if possible_moves:
return minimax(game.board, depth - 1, opposite(player), alpha,
beta) # hand over to opponent, nothing changed
else: # the opponent has no moves either, game over
return pos_score_sum(game.board)
def mobility(board):
# defined number of possible moves : black - white
g1 = Othello()
g1.board = board
g1.current_player = BLACK
score_black = len(g1.find_all_valid_moves())
g1.current_player = WHITE
score_white = len(g1.find_all_valid_moves())
return score_black - score_white
