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.
Python代码:
class Solution:
def overflow(self, x):
"""
:type x: int
:rtype: bool
"""
if x > 0xFFFFFFFF or -x > 0xFFFFFFFF:
return True
return False
def reverse(self, x):
"""
:type x: int
:rtype: int
"""
MAX = 0x7FFFFFFF
MIN = 0x80000000
mask = 0xFFFFFFFF
while (self.overflow(x) and x >= 0):
x -= (mask + 1)
while (self.overflow(x) and x < 0):
x += (mask + 1)
if x >= MIN and x <= mask: #x为负整数
x = -((x ^ mask) + 1) #对x取二进制补码
if x >= 0 and x <= MAX: #x为正整数
x = int(str(x)[::-1])
if x > MAX: #若反转后大于MAX,则溢出
x = 0
elif x < 0 and -x <= MIN:
x = -int(str(x)[:0:-1])
else:
x = 0
if (self.overflow(x) or (x > 0 and x > MAX) or (x < 0 and -x > MIN)):
x = 0
return x