leetcode 150. Evaluate Reverse Polish Notation

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题目链接

思路：逆波兰用栈来做

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class Solution:
    def evalRPN(self, tokens):
        """
        :type tokens: List[str]
        :rtype: int
        """
        stack = []
        for token in tokens:
            if token in '+-*/':
                num2 = stack.pop()
                num1 = stack.pop()
                if token == '+':
                    num = int(num1)+int(num2)
                    stack.append(str(num))
                elif token == '-':
                    num = int(num1)-int(num2)
                    stack.append(str(num))
                elif token == '*':
                    num = int(num1)*int(num2)
                    stack.append(str(num))
                else:
                    num = int(int(num1)/int(num2))
                    stack.append(str(num))
            else:
                stack.append(token)
        return int(stack[0])