class TreeNode: def __init__(self, val=None, left=None, right=None): self.val = val self.left = left self.right = right def infix_to_postfix(infix): operators = {'(': 0, ')': 0, 'NOT': 1, 'AND': 2, 'OR': 3} stack = [] postfix = [] for token in infix: if token in operators: if token == '(': stack.append(token) elif token == ')': while stack[-1] != '(': postfix.append(stack.pop()) stack.pop() else: while stack and operators[stack[-1]] >= operators[token]: postfix.append(stack.pop()) stack.append(token) else: postfix.append(token) while stack: postfix.append(stack.pop()) return postfix def postfix_to_tree(postfix): stack = [] for token in postfix: if token in {'NOT', 'AND', 'OR'}: right = stack.pop() if token == 'NOT': stack.append(TreeNode('NOT', None, right)) else: left = stack.pop() stack.append(TreeNode(token, left, right)) else: stack.append(TreeNode(token)) return stack.pop() def evaluate(root, values): if root.val in values: return values[root.val] elif root.val == 'NOT': return not evaluate(root.right, values) elif root.val == 'AND': return evaluate(root.left, values) and evaluate(root.right, values) elif root.val == 'OR': return evaluate(root.left, values) or evaluate(root.right, values) def print_tree(root, level=0): if root: print_tree(root.right, level + 1) print(' ' * 4 * level + '->', root.val) print_tree(root.left, level + 1) infix = input('请输入命题演算公式：').split() postfix = infix_to_postfix(infix) root = postfix_to_tree(postfix) print('后缀表达式：', postfix) print('二叉树构造过程：') print_tree(root) print('真值表：') variables = list(set(filter(lambda x: x not in {'NOT', 'AND', 'OR'}, infix))) for values in itertools.product([True, False], repeat=len(variables)): values = dict(zip(variables, values)) result = evaluate(root, values) print(values, '->', result)其中有错误NameError: name 'itertools' is not defined。请修改

在代码的开头处添加`import itertools`即可解决该错误：

import itertools

class TreeNode:
    def __init__(self, val=None, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def infix_to_postfix(infix):
    operators = {'(': 0, ')': 0, 'NOT': 1, 'AND': 2, 'OR': 3}
    stack = []
    postfix = []
    for token in infix:
        if token in operators:
            if token == '(':
                stack.append(token)
            elif token == ')':
                while stack[-1] != '(':
                    postfix.append(stack.pop())
                stack.pop()
            else:
                while stack and operators[stack[-1]] >= operators[token]:
                    postfix.append(stack.pop())
                stack.append(token)
        else:
            postfix.append(token)
    while stack:
        postfix.append(stack.pop())
    return postfix

def postfix_to_tree(postfix):
    stack = []
    for token in postfix:
        if token in {'NOT', 'AND', 'OR'}:
            right = stack.pop()
            if token == 'NOT':
                stack.append(TreeNode('NOT', None, right))
            else:
                left = stack.pop()
                stack.append(TreeNode(token, left, right))
        else:
            stack.append(TreeNode(token))
    return stack.pop()

def evaluate(root, values):
    if root.val in values:
        return values[root.val]
    elif root.val == 'NOT':
        return not evaluate(root.right, values)
    elif root.val == 'AND':
        return evaluate(root.left, values) and evaluate(root.right, values)
    elif root.val == 'OR':
        return evaluate(root.left, values) or evaluate(root.right, values)

def print_tree(root, level=0):
    if root:
        print_tree(root.right, level + 1)
        print(' ' * 4 * level + '->', root.val)
        print_tree(root.left, level + 1)

infix = input('请输入命题演算公式：').split()
postfix = infix_to_postfix(infix)
root = postfix_to_tree(postfix)
print('后缀表达式：', postfix)
print('二叉树构造过程：')
print_tree(root)
print('真值表：')
variables = list(set(filter(lambda x: x not in {'NOT', 'AND', 'OR'}, infix)))
for values in itertools.product([True, False], repeat=len(variables)):
    values = dict(zip(variables, values))
    result = evaluate(root, values)
    print(values, '->', result)