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.
思路：对于负数设置一个标志位，然后将其转化成正整数，再来计算，最后判断大小是否超过了[−231, 231 − 1]这个范围。时间复杂度为O(log 10 x), 空间复杂度为O(1)。
代码
1 class Solution(object):
2 def reverse(self, x):
3 """
4 :type x: int
5 :rtype: int
6 """
7 if x == 0: # 为0直接返回
8 return 0
9 res, neg_flag = 0,False # 设置结果和负数标志位
10 if x < 0:
11 neg_flag = True
12 x = abs(x)
13 while x: # 进行反转
14 tem = x % 10
15 x = x// 10
16 res = (res*10 + tem)
17 if neg_flag: # 判断舒服标志位，并进行相应的转换
18 res = 0-res
19 if res > pow(2,31)-1 or res < -pow(2,31): # 判断是否超出范围， 直接返回0
20 return 0
21 return res # 返回结果