def alpha_beta_result(game_state: GameState, max_depth: int, best_black: int,
best_white: int, eval_fn: Callable) -> int:
if game_state.is_over():
return MAX_SCORE if game_state.winner(
) == game_state.next_player else MIN_SCORE
if max_depth == 0:
return eval_fn(game_state)
best_so_far = MIN_SCORE
for candidate_move in game_state.legal_moves():
next_state = game_state.apply_move(candidate_move)
opponent_best_result = alpha_beta_result(next_state, max_depth - 1,
best_black, best_white,
eval_fn)
our_result = -opponent_best_result
if our_result > best_so_far:
best_so_far = our_result
if game_state.next_player == Player.WHITE:
if best_so_far > best_white:
best_white = best_so_far
outcome_for_black = -best_so_far
if outcome_for_black < best_black:
return best_so_far
elif game_state.next_player == Player.BLACK:
if best_so_far > best_black:
best_black = best_so_far
outcome_for_white = -best_so_far
if outcome_for_white < best_white:
return best_so_far
return best_so_far
def best_result(game_state: GameState) -> GameResult:
if game_state.is_over():
if game_state.winner() == game_state.next_player:
return GameResult.Win
elif game_state.winner() is None:
return GameResult.Draw
else:
return GameResult.Loss
best_result_so_far = GameResult.Loss
for candidate_move in game_state.legal_moves():
next_state = game_state.apply_move(candidate_move)
opponent_best_result = best_result(next_state)
our_result = reverse_game_result(opponent_best_result)
if our_result.value > best_result_so_far.value:
best_result_so_far = our_result
return best_result_so_far
def best_result(game_state: GameState, max_depth: int, eval_fn: Callable):
if game_state.is_over():
return MAX_SCORE if game_state.winner(
) == game_state.next_player else MIN_SCORE
if max_depth == 0:
return eval_fn(game_state)
best_so_far = MIN_SCORE
for candidate_move in game_state.legal_moves():
next_state = game_state.apply_move(candidate_move)
opponent_best_result = best_result(next_state, max_depth - 1, eval_fn)
our_result = -1 * opponent_best_result
if our_result > best_so_far:
best_so_far = our_result
return best_so_far