【LeetCode每天一题】Reverse Integer(反转数字)

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

---

 class Solution(object):
     def reverse(self, x):
         """
         :type x: int
         :rtype: int
         """
         if x == :                     # 为0直接返回
             return
         res, neg_flag = ,False         # 设置结果和负数标志位
         if x < :
             neg_flag = True
             x = abs(x)
         while x:                      # 进行反转
             tem = x %
             x = x//
             res = (res* + tem)
         if neg_flag:                   # 判断舒服标志位，并进行相应的转换
             res =  -res
         if res > pow(,)- or res < -pow(,):      # 判断是否超出范围， 直接返回0
             return
         return res                  # 返回结果