Leetcode:7- Reverse Integer

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 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

class Solution(object):
    def reverse(self,x):
        answer = 0
        if x > 0:
            sign = 1
        else:
            sign = -1
        x =  abs(x)
        while x > 0:
            answer = 10 * answer + x % 10  #取x的最后一位算到answer中
            x //= 10  #去掉x的最后一位
        if answer > 2147483648:  #32位int类型的范围为【-2147483648~2147483647】
            return 0
        else:
            return sign*answer

if __name__=='__main__':
    solution = Solution()
    x = 123
    print(solution.reverse(x))