leetcode—— Reverse Integer

要求：给定一个32位有符号整数，取反。

例子：Input: 123 Output: 321

           Input: -123 Output: -321

          Input: 120 Output: 21

思路一：通过数字取反，首先需要判断正负

class Solution(object):def reverse(self, x):""":type x: int:rtype: int"""a=0if x<0:flag=-1else:flag=1x=abs(x)while (x>0):a = a * 10 + x % 10x/=10a=flag*areturn a if a< 2147483648 and a>-2147483648 else 0

思路二：通过字符串切片输出

class Solution(object):def reverse(self, x):""":type x: int:rtype: int"""if x<0:x = str(-x)[::-1]result = -1 * int(x)else:result = int(str(x)[::-1])return result if result< 2147483648 and result>-2147483648 else 0

tips:

   字符串切片：list[start:end:step]

   例如：list=[1,2,3,4,5,6,7,8,9]

              list[1:3:1]='2,3'