leetcode--150

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:

        s = []
        res = 0
        if len(tokens)==1:
            return int(tokens[0])
        for i in range(len(tokens)):
            
            if tokens[i] == "+":
                res = s.pop() + s.pop()
                s.append(res)
            elif tokens[i] == "-":
                s3=s.pop()
                res =s.pop()-s3
                s.append(res)
            elif tokens[i] == "*":
                res = s.pop() * s.pop()
                s.append(res)
            elif tokens[i] == "/":
                s1=s.pop()
                res =int(s.pop()/s1)
                s.append(res)

            else:
                s.append(int(tokens[i]))
        return res