7. Reverse Integer

題目：

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.

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解法 1

class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        if x == 0:
            return x
        else:
            x = str(x)
            if '-' in x:
                x = int('-'+''.join(reversed(x[1::])))
            else:
                x = reversed(x)
                x = int(''.join(x))
            if abs(x) > 2**31:
                return 0
            else:
                return x

解法 2

def reverse(self, x):
    s = str(x)
    res = int('-' + s[1:][::-1]) if s[0] == '-' else int(s[::-1])
    return res if -2147483648 <= res <= 2147483647 else 0