題目描述：

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.

解答原始碼：

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){//當x為負數時也是可以進入while迴圈的
            result=result*10+x%10;
            x/=10;
        }
        return (result<INT_MIN||result>INT_MAX)?0:result;
    }
};