Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123Output:  321

Example 2:

Input: -123Output: -321

Example 3:

Input: 120Output: 21

Note:

Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

题意：翻转整数

思路：需要注意两个问题。（1）翻转后前置0去掉（下述方法不会出现前导0） （2）超出32位int类型的时候输出0。这个范围在【-2147483648~2147483647】即-2^31 ~ 2^31-1

1 class Solution(object): 2     def reverse(self,x): 3         answer = 0 4         if x > 0: 5             sign = 1 6         else: 7             sign = -1 8         x =  abs(x) 9         while x > 0:10             answer = 10 * answer + x % 10  #取x的最后一位算到answer中11             x //= 10  #去掉x的最后一位12         if answer > 2147483648:  #32位int类型的范围为【-2147483648~2147483647】13             return 014         else:15             return sign*answer16 17 if __name__=='__main__':18     solution = Solution()19     x = 12320     print(solution.reverse(x))