说明

用python实现了井字棋，整个框架是本人自己构思的，自认为比较满意。另外，90%+的代码也是本人逐字逐句敲的。

minimax算法还没完全理解，所以参考了这里的代码，并作了修改。

特点

• 可以选择人人、人机、机人、机机四种对战模式之一
• 电脑玩家的AI使用了minimax算法，带apha-beta剪枝
• 电脑玩家在思考时，时时刻刻都有一个“假想敌”。以便使得minimax算法运转起来

代码

作者：hhh5460

时间：2017年6月26日

# 棋盘

class Board(object):

    def __init__(self):

        #self._board = '-'*9 # 坑！！

        self._board = ['-' for _ in range(9)]

        self._history = [] # 棋谱

    # 按指定动作，放入棋子

    def _move(self, action, take):

        if self._board[action] == '-':

            self._board[action] = take

            self._history.append((action, take)) # 加入棋谱

    # 撤销动作，拿走棋子

    def _unmove(self, action):

        self._board[action] = '-'

        self._history.pop()

    # 棋盘快照

    def get_board_snapshot(self):

        return self._board[:]

    # 取棋盘上的合法走法

    def get_legal_actions(self):

        actions = []

        for i in range(9):

            if self._board[i] == '-':

                actions.append(i)

        return actions

    # 判断走法是否合法

    def is_legal_action(self, action):

        return self._board[action] == '-'

    # 终止检测

    def teminate(self):

        board = self._board

        lines = [board[0:3], board[3:6], board[6:9], board[0::3], board[1::3], board[2::3], board[0::4], board[2:7:2]]

        if ['X']*3 in lines or ['O']*3 in lines or '-' not in board:

            return True

        else:

            return False

    # 胜负检查

    def get_winner(self):

        board = self._board

        lines = [board[0:3], board[3:6], board[6:9], board[0::3], board[1::3], board[2::3], board[0::4], board[2:7:2]]

        if ['X']*3 in lines:

            return 0

        elif ['O']*3 in lines:

            return 1

        else:

            return 2

    # 打印棋盘

    def print_b(self):

        board = self._board

        for i in range(len(board)):

            print(board[i], end='')

            if (i+1)%3 == 0:

                print()

    # 打印棋谱

    def print_history(self):

        print(self._history)

# 玩家

class Player(object):

    '''

    玩家只做两件事：思考、落子

        1. 思考 --> 得到走法

        2. 落子 --> 执行走法，改变棋盘

    '''

    def __init__(self, take='X'): # 默认执的棋子为 take = 'X'

        self.take=take

    def think(self, board):

        pass

    def move(self, board, action):

        board._move(action, self.take)

# 人类玩家

class HumanPlayer(Player):

    def __init__(self, take):

        super().__init__(take)

    def think(self, board):

        while True:

            action = input('Please input a num in 0-8:')

            if len(action)==1 and action in '012345678' and board.is_legal_action(int(action)):

                return int(action)

# 电脑玩家

class AIPlayer(Player):

    def __init__(self, take):

        super().__init__(take)

    def think(self, board):

        print('AI is thinking ...')

        take = ['X','O'][self.take=='X']

        player = AIPlayer(take)     # 假想敌！！！

        _, action = self.minimax(board, player)

        #print('OK')

        return action

    # 极大极小法搜索，α-β剪枝

    def minimax(self, board, player, depth=0) :

        '''参考：https://*.com/questions/44089757/minimax-algorithm-for-tic-tac-toe-python'''

        if self.take == "O":

            bestVal = -10

        else:

            bestVal = 10

        if board.teminate() :

            if board.get_winner() == 0 :

                return -10 + depth, None

            elif board.get_winner() == 1 :

                return 10 - depth, None

            elif board.get_winner() == 2 :

                return 0, None

        for action in board.get_legal_actions() : # 遍历合法走法

            board._move(action, self.take)

            val, _ = player.minimax(board, self, depth+1) # 切换到 假想敌！！！

            board._unmove(action) # 撤销走法，回溯

            if self.take == "O" :

                if val > bestVal:

                    bestVal, bestAction = val, action

            else :

                if val < bestVal:

                    bestVal, bestAction = val, action

        return bestVal, bestAction

# 游戏

class Game(object):

    def __init__(self):

        self.board = Board()

        self.current_player = None

    # 生成玩家

    def mk_player(self, p, take='X'): # p in [0,1]

        if p==0:

            return HumanPlayer(take)

        else:

            return AIPlayer(take)

    # 切换玩家

    def switch_player(self, player1, player2):

        if self.current_player is None:

            return player1

        else:

            return [player1, player2][self.current_player == player1]

    # 打印赢家

    def print_winner(self, winner): # winner in [0,1,2]

        print(['Winner is player1','Winner is player2','Draw'][winner])

    # 运行游戏

    def run(self):

        ps = input("Please select two player's type:\n\t0.Human\n\t1.AI\nSuch as:0 0\n")

        p1, p2 = [int(p) for p in ps.split(' ')]

        player1, player2 = self.mk_player(p1, 'X'), self.mk_player(p2, 'O') # 先手执X，后手执O

        print('\nGame start!\n')

        self.board.print_b() # 显示棋盘

        while True:

            self.current_player = self.switch_player(player1, player2) # 切换当前玩家

            action = self.current_player.think(self.board) # 当前玩家对棋盘进行思考后，得到招法

            self.current_player.move(self.board, action)   # 当前玩家执行招法，改变棋盘

            self.board.print_b() # 显示当前棋盘

            if self.board.teminate(): # 根据当前棋盘，判断棋局是否终止

                winner = self.board.get_winner() # 得到赢家 0,1,2

                break

        self.print_winner(winner)

        print('Game over!')

        self.board.print_history()

if __name__ == '__main__':

    Game().run()

效果图

下图是人人对战的结果