150. Evaluate Reverse Polish Notation(逆波兰表达式)

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

class Solution:
    def evalRPN(self, tokens):
        """
        :type tokens: List[str]
        :rtype: int
        """
        stack = []
        for i in tokens:
            if i not in ['+','-','*','/']:
                stack.append(i)
            else:
                v2 = int(stack.pop())
                v1 = int(stack.pop())
                if i=='+':
                    stack.append(v1+v2)
                if i=='-':
                    stack.append(v1-v2)
                if i=='*':
                    stack.append(v1*v2)
                if i=='/':
                    stack.append(v1/v2)
        return int(stack[0])