LeetCode | Easy- 7. Reverse Integer | Python3

Description

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.

Answer - Beats 97.98%

class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        if x >= 0 and x <= 2**31-1:
            list_a = list(str(x)[::-1])
            expect = int(''.join(list_a))
            if expect <= 2**31-1:
                return expect
            else:
                return 0
        elif x < 0 and x >= (-2)**31:
            list_a = list(str(abs(x))[::-1])
            expect = -1 * int(''.join(list_a))
            return 0 if expect < (-2)**31 else expect 
        else: 
            return 0        

摘录一个别人的两行答案，beats 97.98%：

class Solution:
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        n = int(str(abs(x))[::-1])   
        return 0 if x == 0 else ((x>0)-(x<0)) * n * (n < 2**31)  

Python3的(x>0)-(x<0) 相当于python2的cmp(). 

# Python program to demonstrate the 
# use of cmp() method
 
# when a<b
a = 1
b = 2
print(cmp(a, b))  
==> -1

# when a = b 
a = 2
b = 2
print(cmp(a, b))  
== > 0

# when a>b 
a = 3
b = 2
print(cmp(a, b))
==> 1