Question 1：
Reverse digits of an integer.Example1:x = 123, return 321 Example2:x = -123, return -321
Note:
The input is assumed to be a 32-bit signed integer. Your function should return 0 when the reversed integer overflows.
Answer：
- method 1：
note：Math.abs, Math.pow；ps: 此方法用字符串处理，有点怪怪的~~但速度较快~~
- method 2 ：
note：直接数据运算，但运行速度不够快~~
