LeetCode_7.Reverse Integer

摘要： 問題 Given a 32-bit signed integer, reverse digits of an integer. Example 1: Input: 123 Output: 321 Example 2: Input: -123 ...

問題

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.

解題

def reverse(x):
"""
:type x: int
:rtype: int
"""
y = -x if x < 0 else x

list = []
last = y
while last > 0:
list.append(last % 10)
last //= 10

sum = 0
length = len(list)
for l in list:
length -= 1
sum += l * 10 ** length

result = -sum if x < 0 else sum

if result > 2147483647 or result < -2147483648:
return 0

return result

思路

這裡利用了不斷對10作除法，所獲得的餘數順序正好與原數字相反的特性。