def alphabeta(player, board, alpha, beta, depth):
if depth == 0:
return othellogame.weighted_score(player, board), None
def value(board, alpha, beta):
return -alphabeta(othellogame.opponent(player), board, -beta, -alpha,
depth - 1)[0]
moves = othellogame.list_legal_moves(player, board)
if not moves:
if not othellogame.any_legal_move(othellogame.opponent(player), board):
return final_value(player, board), None
return value(board, alpha, beta), None
best_move = moves[0]
for move in moves:
if alpha >= beta:
break
val = value(othellogame.make_move(move, player, list(board)), alpha,
beta)
if val > alpha:
alpha = val
best_move = move
return alpha, best_move
def expectimax_value(board, depth, player):
valid_moves = othellogame.list_legal_moves(player, board)
if depth == 0 or not valid_moves:
return othellogame.weighted_score(player, board), None
length_moves = len(valid_moves)
exp_val = 0
for valid_move in valid_moves:
board[valid_move] = str(player)
opponent_player = othellogame.opponent(player)
max_val, best_move = maximum_value(board, depth - 1,
opponent_player)
board[valid_move] = '.'
exp_val += max_val
return exp_val / length_moves, None
def maximum_value(board, depth, player):
valid_moves = othellogame.list_legal_moves(player, board)
if depth == 0 or not valid_moves:
return othellogame.weighted_score(player, board), None
max_value = -100000
best_move = valid_moves[0]
for valid_move in valid_moves:
board[valid_move] = str(player)
opponent_player = othellogame.opponent(player)
exp_val, score = expectimax_value(board, depth - 1,
opponent_player)
board[valid_move] = '.'
if exp_val > max_value:
max_value = exp_val
best_move = valid_move
return max_value, best_move
def minimax(player, board, depth):
def value(board):
return -minimax(othellogame.opponent(player), board, depth - 1)[0]
if depth == 0:
score = othellogame.score(player, board)
return score[0] - score[1], None
moves = othellogame.list_legal_moves(player, board)
if not moves:
if not othellogame.any_legal_move(othellogame.opponent(player), board):
return final_value(player, board), None
return value(board), None
return max((value(othellogame.make_move(k, player, list(board))), k)
for k in moves)
def random_strategy(player, board):
"""A strategy that always chooses a random legal move."""
return random.choice(othellogame.list_legal_moves(player, board))