首先使用一个函数完成输入中序转后序
中序转后序前面的博客有写
Python使用栈将中序转后序（代码）
from pythonds.basic import Stack # 引入栈
def infix_to_postfix(infix_expr):
prec = {}
prec["*"] = 3
prec["/"] = 3
prec["+"] = 2
prec["-"] = 2
prec["("] = 1
op_stack = Stack()
postfix_list = []
# tokenList = infixexpr.split()
token_list = list(infix_expr)
numb = 0
for token in token_list:
if token in "0123456789":
numb = numb * 10 + int(token) # 这里针对多位数
else:
if numb != 0:
postfix_list.append(numb)
numb = 0
if token == '(':
op_stack.push(token)
elif token == ')':
top_token = op_stack.pop()
while top_token != '(':
postfix_list.append(top_token)
top_token = op_stack.pop()
else:
while (not op_stack.isEmpty()) and (prec[op_stack.peek()] >= prec[token]):
postfix_list.append(op_stack.pop())
op_stack.push(token)
while not op_stack.isEmpty():
postfix_list.append(op_stack.pop())
return postfix_list
# return " ".join(postfixList)
print(infix_to_postfix("(11+22)*(13+4)"))
然后使用后序进行计算
def postfix_evaluate(postfix_expr): # 读进来要求是后序表达式
operand_stack = Stack() # 实例化栈（operand：操作数）
for token in postfix_expr:
if isinstance(token, int):
# isinstance() 函数来判断一个对象是否是一个已知的类型，类似 type()
operand_stack.push(int(token)) # 是数字就入栈
else:
operand2 = operand_stack.pop()
operand1 = operand_stack.pop()
# 取出堆栈上面的两个数
result = do_math(token, operand1, operand2)
# 调用函数进行运算
operand_stack.push(result) # 将结果入栈
return operand_stack.pop() # 返回最终运算结束后栈的内容，即返回计算结果
def do_math(op, op1, op2):
if op == "*":
return op1 * op2
elif op == "/":
return op1 / op2
elif op == "+":
return op1 + op2
else:
return op1 - op2
print(postfix_evaluate(infix_to_postfix("(11+22)*(13+4)")))
