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：對於負數設置一個標誌位，然後將其轉化成正整數，再來計算，最後判斷大小是否超過了[−2³¹

代碼

 1 class Solution(object):
 2     def reverse(self, x):
 3         """
 4         :type x: int
 5         :rtype: int
 6         """
 7         if x == 0:                     # 為0直接返回
 8             return 0
 9         res, neg_flag = 0
 
,False         # 設置結果和負數標誌位
10         if x < 0:
11             neg_flag = True
12             x = abs(x)
13         while x:                      # 進行反轉
14             tem = x % 10
15             x = x// 10
16             res = (res*10 + tem)  
17         if neg_flag:                   # 判斷舒服標誌位，並進行相應的轉換
18             res =  0-res
19         if res > pow(2,31)-1 or res < -pow(2,31):      # 判斷是否超出範圍， 直接返回0
20             return 0
21         return res                  # 返回結果

【LeetCode每天一題】Reverse Integer(反轉數字)