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.

开始考虑直接比较反转前后的数是否相等，但考虑到会溢出。于是考虑不断地取第一位和最后一位（10 进制下）进行比较，相等则取第二位和倒数第
二位，直到完成比较或者中途找到了不一致的位。

class Solution {
public:
    bool isPalindrome(int x) {
        if(x<0)
            return false;
        int d=1;
        while(x/d>=10)
            d*=10;
        while(x>0)
        {
            int q=x/d;
            int r=x%10;
            if(q!=r)
            return false;
            x=x%d/10;
            d/=100;
        }
        return true;
        
    }
};