7. Reverse Integer

Reverse digits of an integer.
Example1:x = 123, return 321
Example2:x = -123, return -321

Have you thought about this?
Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!
If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.
Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of 1000000003 overflows. How should you handle such cases?
For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

正负号这个事情， 关键在于  -45 %10 == -5   负数模除 一个数得负数！！！！

public int reverse(int x) {
       int result = 0;
       while(x != 0){
               int tail  = x % 10;
               int newret = result*10 + tail;
               if((newret - tail)/10 != result){  // overflow 判断
                    return 0;
               }
               result = newret;
               x /= 10;
       }
       return result;
}