7. Reverse Integer（翻转整数）

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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 hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

用的是Python 转换成str ,然后翻转，需要注意

1.翻转之后如果溢出，输出0

 class Solution:

     def reverse(self, x):
         """
         :type x: int
         :rtype: int
         """
         neg = x<0
         res = int(''.join(str(abs(x))[::-1]))
         if res > 2**31:
             res = 0
         if neg:
             res = -res
         return res