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 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.

 思路： 将负数取绝对值，都按正整数转化为列表，再将列表转化为正整数，如果x为负则再将所得结果y转化为负数。

class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        list = []
        a = abs(x)
        y = 0
        for i in range(len(str(a))):
            i = a % 10
            list.append(i)
            a = a // 10

        list.reverse()
       
        for j in range(len(list)):
            y = y + list[j]* 10 ** j
        if x < 0:
           y = 0 - y

        if type(x) == type(y) == type(1):  
　　　　　　#if -2147483648<x<2147483648 and -2147483648<y<2147483648  :
            return y
        else:
            return 0