题解 | 牛牛与后缀表达式

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 给定一个后缀表达式，返回它的结果
# @param str string字符串 
# @return long长整型
#
class Solution:
    def legalExp(self, str):
        # write code here
        numlist = []
        num = ""
        for char in str:
            if char.isdigit():
                num += char

            elif char == '#':
                num = int(num)
                numlist.append(num)
                num = ""
            elif char == "+":
                num2 = numlist.pop()
                num1 = numlist.pop()
                numlist.append(num1 + num2)
            elif char == "-":
                num2 = numlist.pop()
                num1 = numlist.pop()
                numlist.append(num1 - num2)
            elif char == "*":
                num2 = numlist.pop()
                num1 = numlist.pop()
                numlist.append(num1 * num2)

        return numlist[0]