题目：

题解：

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        op_to_binary_fn = {
            "+": add,
            "-": sub,
            "*": mul,
            "/": lambda x, y: int(x / y),   # 需要注意 python 中负数除法的表现与题目不一致
        }

        n = len(tokens)
        stack = [0] * ((n + 1) // 2)
        index = -1
        for token in tokens:
            try:
                num = int(token)
                index += 1
                stack[index] = num
            except ValueError:
                index -= 1
                stack[index] = op_to_binary_fn[token](stack[index], stack[index + 1])
            
        return stack[0]