题目描述：
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.
解答源码：
class Solution {
public:
int reverse(int x) {
long long result=0;//long long make res a 64 bit number, the overflow is checked.
while(x){//当x为负数时也是可以进入while循环的
result=result*10+x%10;
x/=10;
}
return (result<INT_MIN||result>INT_MAX)?0:result;
}
};