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[str]) -> int:
        #2+1=3  3*4=12
        # write code here
        list1=[]
        for char in tokens:
            if char in '+-*/':
                a=list1.pop()
                b=list1.pop()
                if char=='+':
                    list1.append(a+b)
                elif char=='-':
                    list1.append(b-a)
                elif char=='*':
                    list1.append(a*b)
                else:
                    list1.append(int(b/a))
            else:
                list1.append(int(char))
        return list1[0]                            
        # list1=[]
        # for char in tokens:
        #     if char=='+'and len(list1)>=2:
        #         a=list1.pop()
        #         b=list1.pop()
        #         result=a+b
        #         list1.append(result)
        #     elif char=='-' and len(list1)>=2:
        #         a=list1.pop()
        #         b=list1.pop()
        #         result=b-a
        #         list1.append(result)
        #     elif char=='*'and len(list1)>=2:
        #         a=list1.pop()
        #         b=list1.pop()
        #         result=a*b
        #         list1.append(result)
        #     elif char=='/' and len(list1)>=2:
        #         a=list1.pop()
        #         b=list1.pop()
        #         result=a/b
        #         list1.append(result)
        #     else:
        #         list1.append(int(char))    
        # return list1[0]