def negamax_alpha_beta(board: np.ndarray, player: BoardPiece, depth: int,
alpha: float, beta: float) -> float:
"""
Search game tree using alpha-beta pruning with negamax.
:param board: current board state
:param player: current player
:param depth: max depth to search in game tree
:param alpha: alpha value for pruning
:param beta: beta value for pruning
:return:
"""
# if we're at an end state,
if (depth == 0) or check_game_over(board):
return evaluate_end_state(board, player)
# otherwise loop over child nodes
other_player = BoardPiece(player % 2 + 1)
value = -np.inf
for move in get_valid_moves(board):
value = max(
value, -negamax_alpha_beta(
apply_player_action(board, move, player, copy=True),
other_player, depth - 1, -beta, -alpha))
alpha = max(alpha, value)
if alpha >= beta:
break
# print(f'value:{value}')
# print(f'depth = {depth}; end state = {check_game_over(board)}; player = {player}')
# print(f'move:{move}; max value:{value}')
return value
def negamax(
board: np.ndarray,
player: BoardPiece,
depth: int,
) -> float:
"""
Search game tree using plain negamax.
This is "colorless" negamax -- it assumes the heuristic value is from the perspective of the player its called on
:param board: current board state
:param player: current player
:param depth: max depth to search in game tree
:return:
"""
# if we're at an end state,
if (depth == 0) or check_game_over(board):
return evaluate_end_state(board, player)
# otherwise loop over child nodes
other_player = BoardPiece(player % 2 + 1)
value = -np.inf
for move in get_valid_moves(board):
value = max(
value,
-negamax(apply_player_action(board, move, player, copy=True),
other_player, depth - 1))
# print(f'value:{value}')
# print(f'depth = {depth}; end state = {check_game_over(board)}; player = {player}')
# print(f'move:{move}; max value:{value}')
return value
def test_check_game_over():
from agents.common import check_game_over
from agents.common import initialize_game_state
dummy_board = initialize_game_state()
player = PLAYER1
assert check_game_over(dummy_board) is False
horizontal_win_player1 = dummy_board.copy()
horizontal_win_player1[0, 0:4] = PLAYER1
assert check_game_over(horizontal_win_player1) is True
# check a vertical win
vertical_win_player1 = dummy_board.copy()
vertical_win_player1[0:4, 0] = PLAYER1
assert check_game_over(vertical_win_player1) is True
# check a diagonal win
diagonal_win_player1 = dummy_board.copy()
for i in range(4):
diagonal_win_player1[i, i] = PLAYER1
assert check_game_over(diagonal_win_player1) is True
def minimax_value(board: np.ndarray, player: BoardPiece, maxing: bool,
depth: int) -> float:
"""
:param board:
:param player:
:param maxing:
:param depth:
:return:
"""
other_player = BoardPiece(player % 2 + 1)
valid_moves = get_valid_moves(board)
value = 0
if depth == 0 or check_game_over(board):
return evaluate_end_state(board, player)
elif maxing is True:
value = -np.inf
for _, move in enumerate(valid_moves):
# print('Maxing')
# print('move:', move)
MMv = minimax_value(board=apply_player_action(board,
move,
player,
copy=True),
player=player,
maxing=False,
depth=depth - 1)
# print('MM value:', MMv)
value = max(value, MMv)
else:
value = np.inf
for _, move in enumerate(valid_moves):
# print('Mining')
# print('move:', move)
MMv = minimax_value(board=apply_player_action(board,
move,
player,
copy=True),
player=player,
maxing=True,
depth=depth - 1)
# print('MM value:', MMv)
value = min(value, MMv)
return value
def simulate(self, node: MonteCarloNode) -> Union[BoardPiece, GameState]:
"""
Simulate a game from a given node -- outcome is either player or GameState.IS_DRAW
:param node:
:return:
"""
current_rollout_state = node.board.copy()
curr_player = node.to_play
while not check_game_over(current_rollout_state):
possible_moves = get_valid_moves(current_rollout_state)
if possible_moves.size > 1:
action = np.random.choice(list(possible_moves))
else:
action = possible_moves
current_rollout_state = apply_player_action(current_rollout_state, action, curr_player, copy=True)
curr_player = BoardPiece(curr_player % 2 + 1)
return evaluate_end_state(current_rollout_state)
def run_search(self, state: np.ndarray, to_play: BoardPiece, n_sims=3000):
"""
Find an unexpanded, non-terminal node, expand it, simulate a game from it, and backprop the result.
:param state:
:param to_play: which player's turn it is
:param n_sims: iterations to run
:return:
"""
self.make_node(state, to_play)
for _ in range(n_sims):
node = self.select(state, to_play)
if check_game_over(node.board) is False:
node = self.expand(node)
winner = self.simulate(node)
else:
winner = self.simulate(node)
self.backpropagate(node, winner)
def alpha_beta_value(board: np.ndarray, player: BoardPiece, maxing: bool,
depth: int, alpha, beta) -> float:
other_player = BoardPiece(player % 2 + 1)
valid_moves = get_valid_moves(board)
if depth == 0 or check_game_over(board):
return evaluate_end_state(board, player)
elif maxing is True:
value = -np.inf
for _, move in enumerate(valid_moves):
ABv = alpha_beta_value(board=apply_player_action(board,
move,
player,
copy=True),
player=player,
maxing=False,
depth=depth - 1,
alpha=alpha,
beta=beta)
value = max(value, ABv)
alpha = max(alpha, value)
if alpha >= beta:
break
return value
else:
value = np.inf
for _, move in enumerate(valid_moves):
ABv = alpha_beta_value(board=apply_player_action(board,
move,
player,
copy=True),
player=player,
maxing=True,
depth=depth - 1,
alpha=alpha,
beta=beta)
value = min(value, ABv)
beta = min(beta, value)
if beta <= alpha:
break
return value
def is_game_over(self):
"""
Check if this node is a terminal game state (including draws, wins).
:return: Bool
"""
return check_game_over(self.board)
