极大极小算法在Python中不适用井字游戏

Question

我最近试着用minimax(在YouTube的帮助下)创建一个简单的井字棋AI，但我不能让它工作。该算法只输出它检查的第一个值，而不是遍历所有值并给出最佳值。

我试着从YouTube视频中复制代码，但它仍然不起作用，有人能告诉我出了什么问题吗?

import math
import random
print()
board = {1: '   ', 2: '   ', 3: '   ',
4: '   ', 5: '   ', 6: '   ',
7: '   ', 8: '   ', 9: '   '}
computerLetter = 'X'
playerLetter = 'O'

def print_board(board=board):
for i in range(1, 8, 3):
print('|' + board[i] + '|' + board[i + 1] + '|' + board[i + 2] + '|')
if i < 7:
print('-' * 13)
print()

def space_is_free(position):
if board[position] == '   ':
return True
else:
return False

def free_spaces(board=board):
freeSpaces = 0
for key in board.keys():
if key == '   ':
freeSpaces += 1
return freeSpaces

def make_move(letter, position):
if space_is_free(position):
board[position] = ' ' + letter + ' '
print_board(board)
if check_for_win(board):
if letter == 'O':
print("You win!!")
exit()
else:
print("The computer wins. Better luck next time!")
exit()
elif check_for_tie(board):
print("It's a tie! Well played.")
exit()
else:
print("Invalid choice.")
position = int(input("Enter new position: "))
make_move(letter, position)

def check_for_win(board=board):
if board[1] == board[2] == board[3] != '   ' or board[4] == board[5] == board[6] != '   ' or board[7] == board[8] 
== board[9] != '   ' or board[1] == board[4] == board[7] != '   ' or board[2] == board[5] == board[6] != 
'   ' or board[3] == board[6] == board[9] != '   ' or board[1] == board[5] == board[9] != '   ' or board[3]
== board[5] == board[7] != '   ':
return True
else:
return False

def check_for_win_letter(letter):
if board[1] == board[2] == board[3] == ' ' + letter + ' ' or board[4] == board[5] == board[6] == ' ' + letter + ' '
or board[7] == board[8] == board[9] == ' ' + letter + ' ' or board[1] == board[4] or board[7] == ' ' +
letter + ' ' or board[2] == board[5] or board[6] == ' ' + letter + ' ' or board[3] == board[6] or board[9]
== ' ' + letter + ' ' or board[1] == board[5] == board[9] == ' ' + letter + ' ' or board[3] == board[5] ==
board[7] == ' ' + letter + ' ':
return True
else:
return False

def check_for_tie(board=board):
for key in board.keys():
if board[key] == '   ':
return False
else:
return True

def player_move(playerLetter='O'):
if free_spaces(board) >= 9:
print_board(board)
position = int(input("Enter position (1-9): "))
make_move(playerLetter, position)

def computer_move(computerLetter='X'):
if free_spaces(board) == 9:
make_move(computerLetter, 5)
else:
bestScore = -math.inf
bestPosition = 0
for key in board.keys():
if space_is_free(key):
board[key] = ' ' + computerLetter + ' '
score = minimax(board, 0, False)
board[key] = '   '
if score > bestScore:
bestScore = score
bestPosition = key
make_move(computerLetter, bestPosition)
print(f"Computer moves to {bestPosition}.")

def minimax(board, depth, isMaximising):
if check_for_win_letter('X'):
return 1 * (free_spaces(board) + 1)
elif check_for_win_letter('O'):
return -1 * (free_spaces(board) + 1)
elif check_for_tie(board):
return 0
if isMaximising:
bestScore = -math.inf
for key in board.keys():
if space_is_free(key):
board[key] = ' ' + computerLetter + ' '
score = minimax(board, depth + 1, False)
board[key] = '   '
bestScore = max(score, bestScore)
return bestScore
else:
bestScore = math.inf
for key in board.keys():
if space_is_free(key):
board[key] = ' ' + playerLetter + ' '
score = minimax(board, depth + 1, True)
board[key] = '   '
bestScore = min(score, bestScore)
return bestScore

while not check_for_win(board):
computer_move('X')
player_move('O')
# gameState = input("Would you like to play again? (y/n)")
#
# if gameState.lower() == 'y':
#     main()
# elif gameState.lower() == 'n':
#     exit()
# else:
#     print("Invalid choice.")

我试着改变电脑和球员的字母，以及电脑是最大化还是最小化，但它没有工作。

Answer 1

我想我已经找到了你的代码有什么问题，在minmax函数中，第一个if, elif, else语句总是以返回语句结束。

def minimax(board, depth, isMaximising):
if check_for_win_letter('X'):
return 1 * (free_spaces(board) + 1)
elif check_for_win_letter('O'):
return -1 * (free_spaces(board) + 1)
elif check_for_tie(board):
return 0

else语句是失败的原因。

当一个return语句被调用时，它结束函数返回所声明的变量，在这种情况下，它总是一个介于-9和9之间的数字，并且不运行下一个代码块，破坏了计算机寻找最佳/最差位置的过程。else语句意味着即使前面的语句为假，它也将始终返回零，结束函数并停止下一个代码块的处理。

我希望这对你有帮助!:)

Answer 2

好了，我知道问题出在哪里了，实际上是在检查获胜者和获胜者字母的函数中出现了一堆逻辑错误，每说几句错字。

错误1:

def check_for_win(board=board):
if board[1] == board[2] == board[3] != '   ' or board[4] == board[5] == board[6] != '   ' or board[7] == board[8] 
== board[9] != '   ' or board[1] == board[4] == board[7] != '   ' or ****board[2] == board[5] == board[6]**** !=  # board[6] should be board[8]
'   ' or board[3] == board[6] == board[9] != '   ' or board[1] == board[5] == board[9] != '   ' or board[3]
== board[5] == board[7] != '   ':
return True

错误2:

def check_for_win_letter(letter):
if board[1] == board[2] == board[3] == ' ' + letter + ' ' or board[4] == board[5] == board[6] == ' ' + letter + ' '
or board[7] == board[8] == board[9] == ' ' + letter + ' ' or board[1] == board[4] ****or board[7]**** == ' ' +
letter + ' ' or board[2] == board[5] ****or board[6]**** == ' ' + letter + ' ' or board[3] == board[6] ****or board[9]****
== ' ' + letter + ' ' or board[1] == board[5] == board[9] == ' ' + letter + ' ' or board[3] == board[5] ==
board[7] == ' ' + letter + ' ':
return True

星号(*)内的语句为错误，or语句应为==,board[6]应再次为board[8]。