我最近报名参加了CS50人工智能Python课程,其中一个要做的项目是为一个小游戏实现一个极小值算法。我寻求帮助并搜索了stackoverflow,但我没有找到一个可以帮助我的答案。它的图形部分已经实现了,你所需要做的就是对模板的给定函数进行编程,我相信我是对的,除了算法部分,函数如下:
import math
import copy
X = "X"
O = "O"
EMPTY = None
def initial_state():
"""
Returns starting state of the board.
"""
return [[EMPTY, EMPTY, EMPTY],
[EMPTY, EMPTY, EMPTY],
[EMPTY, EMPTY, EMPTY]]
def player(board):
"""
Returns player who has the next turn on a board.
"""
if board == initial_state():
return X
xcounter = 0
ocounter = 0
for row in board:
xcounter += row.count(X)
ocounter += row.count(O)
if xcounter == ocounter:
return X
else:
return O
def actions(board):
"""
Returns set of all possible actions (i, j) available on the board.
"""
possible_moves = []
for i in range(3):
for j in range(3):
if board[i][j] == EMPTY:
possible_moves.append([i, j])
return possible_moves
def result(board, action):
"""
Returns the board that results from making move (i, j) on the board.
"""
boardcopy = copy.deepcopy(board)
try:
if boardcopy[action[0]][action[1]] != EMPTY:
raise IndexError
else:
boardcopy[action[0]][action[1]] = player(boardcopy)
return boardcopy
except IndexError:
print('Spot already occupied')
def winner(board):
"""
Returns the winner of the game, if there is one.
"""
columns = []
# Checks rows
for row in board:
xcounter = row.count(X)
ocounter = row.count(O)
if xcounter == 3:
return X
if ocounter == 3:
return O
# Checks columns
for j in range(len(board)):
column = [row[j] for row in board]
columns.append(column)
for j in columns:
xcounter = j.count(X)
ocounter = j.count(O)
if xcounter == 3:
return X
if ocounter == 3:
return O
# Checks diagonals
if board[0][0] == O and board[1][1] == O and board[2][2] == O:
return O
if board[0][0] == X and board[1][1] == X and board[2][2] == X:
return X
if board[0][2] == O and board[1][1] == O and board[2][0] == O:
return O
if board[0][2] == X and board[1][1] == X and board[2][0] == X:
return X
# No winner/tie
return None
def terminal(board):
"""
Returns True if game is over, False otherwise.
"""
# Checks if board is full or if there is a winner
empty_counter = 0
for row in board:
empty_counter += row.count(EMPTY)
if empty_counter == 0:
return True
elif winner(board) is not None:
return True
else:
return False
def utility(board):
"""
Returns 1 if X has won the game, -1 if O has won, 0 otherwise.
"""
if winner(board) == X:
return 1
elif winner(board) == O:
return -1
else:
return 0
def minimax(board):
current_player = player(board)
if current_player == X:
v = -math.inf
for action in actions(board):
k = min_value(result(board, action)) #FIXED
if k > v:
v = k
best_move = action
else:
v = math.inf
for action in actions(board):
k = max_value(result(board, action)) #FIXED
if k < v:
v = k
best_move = action
return best_move
def max_value(board):
if terminal(board):
return utility(board)
v = -math.inf
for action in actions(board):
v = max(v, min_value(result(board, action)))
return v #FIXED
def min_value(board):
if terminal(board):
return utility(board)
v = math.inf
for action in actions(board):
v = min(v, max_value(result(board, action)))
return v #FIXED
最后一部分是minimax(棋盘)函数所在的位置,它应该获取棋盘的当前状态,并根据AI是玩家“X”还是“O”(可以是两者中的任意一个)计算出可能的最佳移动,“X”玩家试图最大化分数,“O”应该利用效用(棋盘)函数最小化分数,该函数返回1表示X赢、-1表示“O”赢或0表示平局。到目前为止,人工智能的移动不是最优的,我可以轻松地在我不应该的时候战胜它,因为在最好的情况下,我应该得到的是一个平局,因为人工智能应该在这一点上计算每一个可能的移动。但我不知道怎么了。。。
首先谈谈调试:如果要打印递归调用中完成的计算,可以跟踪问题的执行情况并快速找到答案。
但是,你的问题似乎是最重要的。在你的极小值调用中,如果当前玩家是X,你就调用该状态的每个子级的max_value,然后取结果的最大值。然而,这在树的顶部应用了两次max函数。游戏中的下一个玩家是O,所以您应该为下一个玩家调用min_value函数。
因此,在minimax调用中,如果当前_播放器为X,则应调用minu value;如果当前_播放器为O,则应调用max_value。
@cs50项目页面上说,harsh kothari
重要的是,原始板应该保持不变:因为极小值最终需要在计算过程中考虑许多不同的板状态。这意味着简单地更新单元格本身并不是结果函数的正确实现。在进行任何更改之前,您可能希望首先对董事会进行深度复制。
为了避免子列表被修改,我们使用深度复制而不是复制
在此处阅读有关copy()和deepcopy()的更多信息
将操作(板)代码更改为
possibleActions = set()
for i in range(0, len(board)):
for j in range(0, len(board[0])):
if board[i][j] == EMPTY:
possibleActions.add((i, j))
return possibleActions