## 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 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.

Thoughts:

1. Use String:
1. sign:
2. reverse abs value: sign * x [::-1]
3. s * r* (r < 2 ^31)
2. Not use string: Standard way of detecting overflow
``````class Solution(object):
def reverse(self, x):
"""
:type x: int
:rtype: int
"""
#sign
s = cmp(x,0)
# reverse abs
r = int(`s*x`[::-1])
return s * r * (r < 2 ** 31)
``````
``````class Solution {
public int reverse(int x){
int result = 0;

while (x != 0)
{
int tail = x % 10;
int newResult = result * 10 + tail;
if ((newResult - tail) / 10 != result) return 0;
result = newResult;
x /= 10;
}
return result;
}
}
``````