题目：

题解：

func evalRPN(tokens []string) int {
    stack := make([]int, (len(tokens)+1)/2)
    index := -1
    for _, token := range tokens {
        val, err := strconv.Atoi(token)
        if err == nil {
            index++
            stack[index] = val
        } else {
            index--
            switch token {
            case "+":
                stack[index] += stack[index+1]
            case "-":
                stack[index] -= stack[index+1]
            case "*":
                stack[index] *= stack[index+1]
            default:
                stack[index] /= stack[index+1]
            }
        }
    }
    return stack[0]
}