9 Palindrome Number

链接：https://leetcode.com/problems/palindrome-number/
问题描述：
Determine whether an integer is a palindrome. Do this without extra space.

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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.

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求一个数字是不是回文数字。负数有没有回文数，所以遇到负数就可以返回false。一种比较好的解决方式是倒置数字，看看倒置的数字是不是和当前的数字相等，如果相等就可以认定这个数字是回文数字。倒置数字连接如下：Reverse Integer http://blog.csdn.net/efergrehbtrj/article/details/46606257

class Solution {
public:
    bool isPalindrome(int x) {
         if(x<0)
             return false;
        return x==reverse(x);
    }
     int reverse(int x) {
        long long int result=0; 

        while(x!=0)
        {
            result=result*10 + x%10;  
            x/=10;
        }
        if(result> INT_MAX|| result< INT_MIN)
            return 0;
        else
            return result;
    }
};

当然还有一种方式是每次取数字最高为或者最低位开始比较。相比较后如果相等则去掉数字的最高位和最低位重复操作。最后数字为0或者只剩下一位。

class Solution {
public:
    bool isPalindrome(int x) {
         if(x<0)
             return false;
         if(x<10)
             return true;
          //21 4748 3647
          int i=9;
          while(x/(int)pow(10,i)==0)
              i--;
          while(i>0)
          {
             if(x/(int)pow(10,i)!=x%10)
                return false;
             else
             {
                x=x%(int)pow(10,i);
                x=x/10;
                i-=2;
             }
          }
          return true;
    }
};