题目描述：
Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
Example 1:
Input: 121 Output: true
Example 2:
Input: -121 Output: false Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
Example 3:
Input: 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
Follow up:
Coud you solve it without converting the integer to a string?
代码如下：
class Solution {
public:
bool isPalindrome(int x) {
int revhalf=0;
int slow=x,fast=x;
//revhalf是将slow即x反转一半后的值，然后将slow和revhalf比较
if(x<0||(x>0&&x%10==0))return false;//如果最后一位为0也不可能为回文数
while(fast){
revhalf=revhalf*10+slow%10;
slow/=10;
fast/=100;
}
//如果x是奇位数，则slow等于（revhalf/10）,如果slow是偶位数，则slow等于revhalf
return slow==revhalf||slow==(revhalf/10);
}
};