蒙特卡洛树搜索在Python中实现井字游戏的完整实例
时间: 2024-11-04 16:15:30 浏览: 42
蒙特卡洛树搜索(Monte Carlo Tree Search, MCTS)是一种基于随机模拟的技术,在下棋类游戏中寻找最佳策略。在井字游戏中,我们可以利用MCTS来构建玩家的决策过程。下面是一个简单的Python实现例子:
```python
import random
# 定义井字游戏的状态表示
class TicTacToeState:
def __init__(self):
self.board = [[' ' for _ in range(3)] for _ in range(3)]
self.winner = None
def make_move(self, player, row, col):
if self.board[row][col] != ' ':
raise ValueError("Position already taken")
self.board[row][col] = player
# 检查游戏是否结束
self.check_win()
def check_win(self):
# 省略检查所有胜利条件的代码
pass # 可以通过遍历所有可能的行、列、对角线判断胜负
# MCTS节点类
class Node:
def __init__(self, state):
self.state = state
self.children = {}
self.visits = 0
self.win_rate = 0
def expand(self):
# 添加一个新位置并返回新的节点
# 这里可以随机选择一个未占用的位置
row, col = random.choice([(i, j) for i in range(3) for j in range(3) if self.state.board[i][j] == ' '])
child_state = TicTacToeState(self.state)
child_state.make_move('X', row, col) if self.state.player == 'O' else child_state.make_move('O', row, col)
return Node(child_state)
def simulate(self):
while True:
# 决策阶段
current_node = self
while not current_node.is_leaf():
best_child = max(current_node.children.values(), key=lambda node: node.win_rate)
current_node = best_child
# 执行随机动作
current_node.execute_random_move()
# 后期计算阶段
if current_node.state.winner is not None:
current_node.update_win_rate()
def execute_random_move(self):
# 随机选择一个孩子节点并访问它
child = random.choice(list(self.children.keys()))
self.visit(child)
def update_win_rate(self):
self.win_rate += 1 if self.state.winner == self.state.player else -1
self.visits += 1
@property
def is_leaf(self):
return len(self.children) == 0
def visit(self, node):
if node not in self.children:
self.children[node] = Node(node.state)
self.children[node].visits += 1
self.win_rate += self.state.winner == self.state.player
# 使用MCTS进行决策
def mcts_play(board, player='X'):
root = Node(TicTacToeState(board))
for _ in range(100): # 进行多次迭代,调整次数以获得更好的策略
node = root
node.expand()
node.simulate()
# 返回当前看起来最好的下一步
best_move = max(root.children.items(), key=lambda item: item[1].win_rate)[0]
return best_move
# 示例游戏开始
state = TicTacToeState()
state.player = 'X'
state.board = [[' ']*3 for _ in range(3)]
print("X's turn:")
best_move = mcts_play(state.board)
row, col = best_move
state.make_move('X', row, col)
```
这个例子中,我们首先定义了`TicTacToeState`类来表示游戏状态,然后创建了一个`Node`类来表示MCTS的树结构。`mcts_play`函数负责整个MCTS流程,包括节点扩展、模拟和更新。
注意这只是一个简化的版本,实际应用中可能需要更复杂的评估函数、剪枝策略等优化。
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