def min_value(self, board: Board, depth, alpha, beta):
"""
function MIN-VALUE(state, alpha, beta) returns a utility value
if TERMINAL-TEST(state) the return UTILITY(state)
v <- +infinity
for each a in ACTIONS(state) do
v <- MIN(v, MAX-VALUE(RESULT(state, a), alpha, beta))
if v <= alpha then return v
beta <- MIN(beta, v)
return v
"""
if self.time_left() < self.TIMER_THRESHOLD:
raise SearchTimeout()
mini = self
if board.is_winner(mini) or board.is_loser(mini):
return board.utility(mini)
if depth <= 0:
# what is the score function of the opponent? certainly not ours!
return self.score(board, mini)
min_value = math.inf
for move in board.get_legal_moves():
min_value = min(
min_value,
self.max_value(board.forecast_move(move), depth - 1, alpha,
beta))
if min_value <= alpha:
return min_value
beta = min(beta, min_value)
return min_value
def max_value(self, board: Board, depth, alpha, beta):
"""
function MAX-VALUE(state, alpha, beta) returns a utility value
if TERMINAL-TEST(state) the return UTILITY(state)
v <- -infinity
for each a in ACTIONS(state) do
v <- MAX(v, MIN-VALUE(RESULT(state, a), alpha, beta))
if v >= beta then return v
alpha <- MAX(alpha, v)
return v
"""
if self.time_left() < self.TIMER_THRESHOLD:
raise SearchTimeout()
maxi = self
if board.is_winner(maxi) or board.is_loser(maxi):
return board.utility(maxi)
if depth <= 0:
return self.score(board, maxi)
max_value = -math.inf
for move in board.get_legal_moves():
max_value = max(
max_value,
self.min_value(board.forecast_move(move), depth - 1, alpha,
beta))
if max_value >= beta:
return max_value
alpha = max(alpha, max_value)
return max_value
def min_value(self, board: Board, depth):
"""
function MIN-VALUE(state) returns a utility value
if TERMINAL-TEST(state) then return UTILITY(state)
v <- infinity
for each a in ACTIONS(state) do
v <- MIN(v, MAX-VALUE(RESULT(state, a)))
return v
"""
if self.time_left() < self.TIMER_THRESHOLD:
raise SearchTimeout()
mini = self
if board.is_winner(mini) or board.is_loser(mini):
return board.utility(mini)
if depth <= 0:
return self.score(board, mini)
min_value = math.inf
for move in board.get_legal_moves():
min_value = min(
min_value, self.max_value(board.forecast_move(move),
depth - 1))
return min_value
def max_value(self, board: Board, depth):
"""
function MAX-VALUE(state) returns a utility value
if TERMINAL-TEST(state) then return UTILITY(state)
v <- -infinity
for each a in ACTIONS(state) do
v <- MAX(v, MIN-VALUE(RESULT(state, a)))
return v
"""
if self.time_left() < self.TIMER_THRESHOLD:
raise SearchTimeout()
maxi = self
utility = board.utility(maxi)
if utility != 0:
return utility
if depth <= 0:
return self.score(board, maxi)
max_value = -math.inf
for move in board.get_legal_moves():
max_value = max(
max_value, self.min_value(board.forecast_move(move),
depth - 1))
return max_value