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])