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.

class Solution {
public:
    int reverse(int x) {
        int64_t res=0; //如果用int会溢出, runtime error
        while(x!=0)
        {
            int tmp=res*10+x%10;
            if((tmp-x%10)/10!=res)
                return 0;
            x/=10;
            res=tmp;
        }
        return res;
    }
};