档案日期2016的1

题目描述：

Given an integer, write a function to determine if it is a power of three.

Follow up:

Could you do it without using any loop / recursion?

题目大意：

给定一个整数，编写函数判断它是否是3的幂。

进一步思考：

你可以不用循环/递归解出本题吗？

解题思路：

解法I：求对数，然后乘方，判断得数是否相等

Python代码：

class ...

题目描述：

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1 ...