7. Reverse Integer

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.

解题要点：

用%10来一位位的加到新整数变量中，同时它本身需要/10。最后需要检测正负数和是否超出整数限制。

class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        neg = False
        if x < 0:
            x = -x
            neg = True
        res = 0
        while x != 0:
            res = res * 10 + x % 10
            x /= 10
        if res > 2**31 - 1:
            return 0
        if neg:
            res = -res
        return res