整数反转 #

给出一个 32 位的有符号整数，你需要将这个整数中每位上的数字进行反转。 示例  1: ``` 输入: 123 输出: 321 ``` 示例 2: ``` 输入: -123 输出: -321 ``` 示例 3: ``` 输入: 120 输出: 21 ``` 注意: 假设我们的环境只能存储得下 32 位的有符号整数，则其数值范围为 \([-2^31, 2^31-1]。\) 请根据这个假设，如果反转后整数溢出那么就返回 0。

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: \([-2^31, 2^31-1].\) For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

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```python class Solution(object): def reverse(self, x): """ :type x: int :rtype: int """ # 符合 s = cmp(x, 0) r = int(str(s * x)[::-1]) return s * r * (r < 2**31) ```

`python3` 没有 `cmp` 函数， 使用 `(a > b) - (a < b)` 替代 参考： - [stackoverflow](https://stackoverflow.com/questions/22490366/how-to-use-cmp-in-python-3) ```python class Solution: def reverse(self, x: int) -> int: s = (lambda a, b: (a > b) - (a < b))(x, 0) r = int(str(s * x)[::-1]) return s * r * (r < 2**31) ```

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