problem：

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

click to show spoilers.

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.

(1)之前求过int型逆序反转。这里检验一个数是否为一个回文数，能够得到一点启示。

（2）逆序反转主要涉及溢出问题的处理，并且反转的空间复杂度能够忽略不计，满足题目要求。

code:

class Solution {
public:
    bool isPalindrome(int x) {
        int b=0;
        int a=x;
        bool flag=true;
        if(a<0)
        {
            bool flag=false;
            a=-x;
        }
        while(a)
        {
            b*=10;
            b+=a%10;
            a=a/10;
        }
        if(b>2147483647)
            return false;
        if(!flag)
            b=-b;
        return (b==x);
           
        
    }
};