Description：
Given a 32-bit signed integer, reverse digits of an integer.
Example 1:
Input: 123 Output: 321
Example 2:
Input: -123 Output: -321
Example 3:
Input: 120 Output: 21
Note：
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
Answer：
Review：
1、数据类型长度 参考：http://blog.sina.com.cn/s/blog_57421ff80100c7g1.html
2、C++ int32位溢出判断 参考：https://blog.csdn.net/hgpenglin/article/details/85008983 、https://blog.csdn.net/u012604810/article/details/80290706
