这段代码有什么问题class Node: def __init__(self, value): self.value = value self.left_child = None self.right_child = None def build_tree(postfix_expr): opstack = [] token_list = postfix_expr.split() for token in token_list: if token in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" : opstack.append(Node(token)) else: right_child = opstack.pop() left_child = opstack.pop() new_node = Node(token) new_node.left_child = left_child new_node.right_child = right_child opstack.append(new_node) return opstack.pop() def evaluate_tree(tree, var_dict): if tree.left_child and tree.right_child: left_value = evaluate_tree(tree.left_child, var_dict) right_value = evaluate_tree(tree.right_child, var_dict) return evaluate_op(tree.value, left_value, right_value) else: return var_dict[tree.value] def evaluate_op(op, left_value, right_value): if op == "&": return left_value and right_value elif op == "|": return left_value or right_value else: return not left_value def calculate(expr, var_dict): postfix_expr = infix_to_postfix(expr) tree = build_tree(postfix_expr) result = evaluate_tree(tree, var_dict) return result
时间: 2024-04-28 15:21:47 浏览: 14
这段代码的问题在于没有提供 infix_to_postfix 函数的实现。因此,我们无法确定整个程序的正确性。另外,我们也无法确定 var_dict 字典包含的键和值,因为该字典在代码中没有被定义。需要注意的是,如果 var_dict 字典中不存在某个变量,则 evaluate_tree 函数会引发 KeyError 异常。
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这是上题的代码:def infix_to_postfix(expression): precedence = {'!': 3, '&': 2, '|': 1, '(': 0} op_stack = [] postfix_list = [] token_list = expression.split() for token in token_list: if token.isalnum(): postfix_list.append(token) elif token == '(': op_stack.append(token) elif token == ')': top_token = op_stack.pop() while top_token != '(': postfix_list.append(top_token) top_token = op_stack.pop() else: # operator while op_stack and precedence[op_stack[-1]] >= precedence[token]: postfix_list.append(op_stack.pop()) op_stack.append(token) while op_stack: postfix_list.append(op_stack.pop()) return ' '.join(postfix_list) class Node: def __init__(self, value): self.value = value self.left_child = None self.right_child = None def build_expression_tree(postfix_expr): operator_stack = [] token_list = postfix_expr.split() for token in token_list: if token.isalnum(): node = Node(token) operator_stack.append(node) else: right_node = operator_stack.pop() left_node = operator_stack.pop() node = Node(token) node.left_child = left_node node.right_child = right_node operator_stack.append(node) return operator_stack.pop() def evaluate_expression_tree(node, variable_values): if node.value.isalnum(): return variable_values[node.value] else: left_value = evaluate_expression_tree(node.left_child, variable_values) right_value = evaluate_expression_tree(node.right_child, variable_values) if node.value == '!': return not left_value elif node.value == '&': return left_value and right_value elif node.value == '|': return left_value or right_value expression = "!a & (b | c)" postfix_expression = infix_to_postfix(expression) expression_tree = build_expression_tree(postfix_expression) variable_values = {'a': True, 'b': False, 'c': True} result = evaluate_expression_tree(expression_tree, variable_values) print(result)
好的,感谢提供代码。以下是针对你的问题的解答:
1. 打印二叉树构造过程
在 build_expression_tree 函数中,operator_stack 列表存储了构建二叉树的过程。我们可以在函数中添加打印语句来查看二叉树构建过程。
代码如下:
```
def build_expression_tree(postfix_expr):
operator_stack = []
token_list = postfix_expr.split()
for token in token_list:
if token.isalnum():
node = Node(token)
operator_stack.append(node)
else:
right_node = operator_stack.pop()
left_node = operator_stack.pop()
node = Node(token)
node.left_child = left_node
node.right_child = right_node
operator_stack.append(node)
# 打印二叉树构建过程
print([i.value for i in operator_stack])
return operator_stack.pop()
```
在运行 build_expression_tree 函数时,将会打印出二叉树构建过程。
2. 打印后缀表达式和二叉树后序遍历序列
在函数 infix_to_postfix 中,postfix_list 列表存储了后缀表达式。我们可以在函数返回后缀表达式的同时,打印出后缀表达式。
代码如下:
```
def infix_to_postfix(expression):
precedence = {'!': 3, '&': 2, '|': 1, '(': 0}
op_stack = []
postfix_list = []
token_list = expression.split()
for token in token_list:
if token.isalnum():
postfix_list.append(token)
elif token == '(':
op_stack.append(token)
elif token == ')':
top_token = op_stack.pop()
while top_token != '(':
postfix_list.append(top_token)
top_token = op_stack.pop()
else:
# operator
while op_stack and precedence[op_stack[-1]] >= precedence[token]:
postfix_list.append(op_stack.pop())
op_stack.append(token)
while op_stack:
postfix_list.append(op_stack.pop())
# 打印后缀表达式
print(f"后缀表达式:{' '.join(postfix_list)}")
return ' '.join(postfix_list)
def build_expression_tree(postfix_expr):
operator_stack = []
token_list = postfix_expr.split()
for token in token_list:
if token.isalnum():
node = Node(token)
operator_stack.append(node)
else:
right_node = operator_stack.pop()
left_node = operator_stack.pop()
node = Node(token)
node.left_child = left_node
node.right_child = right_node
operator_stack.append(node)
# 打印二叉树构建过程
print([i.value for i in operator_stack])
return operator_stack.pop()
expression = "!a & (b | c)"
postfix_expression = infix_to_postfix(expression)
expression_tree = build_expression_tree(postfix_expression)
# 打印二叉树后序遍历序列
print("二叉树后序遍历序列:", end="")
def postorder(node):
if node:
postorder(node.left_child)
postorder(node.right_child)
print(node.value, end=" ")
postorder(expression_tree)
print()
```
在运行程序时,将会先打印出后缀表达式,然后是构建二叉树的过程,最后打印出二叉树的后序遍历序列。
3. 打印二叉树评估过程
在 evaluate_expression_tree 函数中,我们可以添加打印语句来查看二叉树评估的过程。
代码如下:
```
def evaluate_expression_tree(node, variable_values):
if node.value.isalnum():
return variable_values[node.value]
else:
left_value = evaluate_expression_tree(node.left_child, variable_values)
right_value = evaluate_expression_tree(node.right_child, variable_values)
if node.value == '!':
result = not left_value
elif node.value == '&':
result = left_value and right_value
elif node.value == '|':
result = left_value or right_value
# 打印二叉树评估过程
print(f"节点 {node.value} 的值为 {result}")
return result
expression = "!a & (b | c)"
postfix_expression = infix_to_postfix(expression)
expression_tree = build_expression_tree(postfix_expression)
variable_values = {'a': True, 'b': False, 'c': True}
result = evaluate_expression_tree(expression_tree, variable_values)
print(result)
```
在运行程序时,将会先打印出后缀表达式,然后是构建二叉树的过程,接着会打印出二叉树评估的过程。
4. 显示公式真值表
可以通过遍历变量的所有取值,来计算表达式的真值表。
代码如下:
```
expression = "!a & (b | c)"
postfix_expression = infix_to_postfix(expression)
expression_tree = build_expression_tree(postfix_expression)
# 遍历变量的所有可能取值
variable_values = {'a': True, 'b': False, 'c': True}
variable_names = list(variable_values.keys())
print(" ".join(variable_names), expression)
for i in range(2**len(variable_names)):
values = [bool(int(x)) for x in bin(i)[2:].zfill(len(variable_names))]
variable_values = dict(zip(variable_names, values))
result = evaluate_expression_tree(expression_tree, variable_values)
print(" ".join([str(int(x)) for x in values]), int(result))
```
在运行程序时,将会先打印出后缀表达式,然后是构建二叉树的过程,接着会打印出真值表。
class Node: def __init__(self, value): self.value = value self.left = None self.right = None import random # 生成一组随机数 values = [random.randint(1, 100) for _ in range(10)] print(values)解释一下
这是一个Python程序,它定义了一个名为Node的类。这个类有三个属性:value、left、right。__init__函数是一个特殊的函数,它在创建一个新的Node对象时会自动调用。__init__函数接收一个参数value,并将其赋值给Node对象的value属性。left和right属性初始化为None。
这个程序还导入了Python标准库中的random模块,但是并没有使用它。