leetcode.0007. Reverse Integer

leetcode.0007. Reverse Integer

题目

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: [−2^31, 2^31 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

参考答案（python3）:

    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """

        y = 0
        if x > 0: 
            sgn = 1
        else: 
            sgn = -1

        x *= sgn
        while x >= 1:       # x=+(-)0 ,y=0
            y = 10*y + x%10 # 重点，
            x //= 10;       # //= 取整赋值运算
        y *= sgn
        if (y < -2**31 or y > (2**31)-1 ):# 超出范围 ,返回0
            return 0
        return y

更优答案（python3）:

class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """

        neg = x < 0
        num = str(abs(x))
        reversed_num = num[::-1] # 字符串到序， 不用借助列表list.reverse()
        if neg:
            neg_reversed = int("-" + reversed_num)# 直接字符串， 转整数 int()
        else:
            neg_reversed = int(reversed_num)
        if neg_reversed > (2**31 - 1) or neg_reversed < (-2**31): # 超出范围 ,返回0
            neg_reversed = 0
        return neg_reversed