Leetcode 9 - Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

Some hints:
Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem “Reverse Integer”, you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

细节实现题，如提示所述，注意以下几点：
1 - 负数必定不是回文数，直接返回false；
2 - 转换成string类型再做比较使用了额外空间，不满足题意；
3 - Reversing an integer可能导致溢出，因此排除此种方法。

思路：首先比较最高位和最低位，再比较次高位和次低位……直到比较完毕。

class Solution {public:    bool isPalindrome(int x) {        if(x<0) return false;        int d=1;        int high,low; //最高位和最低位        while(x/d>=10){            d *= 10;        }        while(x){            //计算最高位和最低位并进行比较            high = x/d;            low = x%10;            if(high!=low) return false;            //删去已经比较完毕的最高位和最低位            x %= d;            x /= 10;            d /= 100;        }        return true;    }};