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.

My silly solution:

class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        MAX_INT = 2147483647 # 2**31-1
        # MIN_INT = -2147483648 # -2**31
        s = str(abs(x))
        l = []
        l += s
        l.reverse()
        num = int(''.join(l))
        if num > MAX_INT:
            return 0
        if x >= 0:
            return num
        else:
            return -num

kvas's solution(official thinking):

class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        MAX_INT = 2147483647 # 2**31-1
        MIN_INT = -2147483648 # -2**31
        rev = 0
        sign = (x > 0) - (x < 0)
        x = abs(x)

        while x != 0:
            rev = rev * 10 + x % 10
                        
            if rev > MAX_INT or rev < MIN_INT:
                return 0
            
            x //= 10

        return rev * sign