题解 | #逆波兰表达式求值#

#
# 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
#
# 
# @param tokens string字符串一维数组 
# @return int整型
#
class Solution:
    def evalRPN(self,tokens: list) -> int:
        stack = []
        for token in tokens:
            if token not in ['+','-','*','/']:
                stack.append(int(token))
            elif not stack:
                return int(tokens[0])
            else:
                num1 = int(stack.pop())
                num2 = int(stack.pop())

                if token == '+':
                    stack.append(num2 + num1)
                elif token == '-':
                    stack.append(num2 - num1)
                elif token == '*':
                    stack.append(num2 * num1)
                elif token == '/':
                    stack.append(num2 / num1)
        return stack[0] if stack else 0