7. Reverse Integer(python3实现）

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.

class Solution:
    def reverse(self, x: int) -> int:
        flag=0
        if x<0:
            flag=1
        x=abs(x)
        li=list(str(x))
        li.reverse()
        y=int(''.join(li))
        if flag==1 and y<2**31:
            return -y
        elif flag==0 and y<2**31-1:
            return y
        else:
            return 0

abs(x) 函数返回数字的绝对值
数据类型的转换：
list与int不能互相转换
int–>str: str(x),x为int型
str–>int: x=int(s),s为str
str–>list: li=list(s)
list–>str: ‘’.join(li)
list.reverse() 函数用于反向列表中元素，该方法没有返回值，但是会对列表的元素进行反向排序
str.join(sequence)返回通过指定字符连接序列中元素后生成的新字符串