7. Reverse Integer

https://leetcode.com/problems/reverse-integer/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.

Solution:

class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        # check input overflow
        if x > 2**31-1: return 0
        if x < -2**31: return 0
        
        inputs = x
        
        if x < 0:
            x *= (-1)
        
        re = 0
        s = str(x)
        i = len(s)
        for ss in s:
            re += int(ss)*10**(len(s)-i)
            i -= 1
        if inputs < 0:
            re *= (-1)
        
        # check output overflow
        if re > 2**31-1: return 0
        if re < -2**31: return 0
        return re