9.回文数

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?

知识补充：

数学公式函数

#include<cmath> double log (double); //以e为底的对数double log10 (double);//log2(N)=log10(N)/log10(2);//log(N)以10为底：log10(N)但没有以2为底的函数但是可以用换底公式int abs();//绝对值函数int pow(x,y);//幂函数x为底，y为指数int digits = 1 + (int)log10(abs(x));//计算位数

测试代码：

bool isPalindrome(int x) {        if(x>=INT_MAX||x<0)        {            return false;        }        if(x==0)        {            return true;        }        int n = (int)log10(abs(x));        int a,b=0;        int pos = n;        while(pos>=n-pos)        {            a = x/(int)pow(10,pos)%10;            b = x%(int)pow(10,n-pos+1)/(int)pow(10,n-pos);            if(a!=b)                return false;            pos--;        }        return true;        }

性能：

参考答案：

bool isPalindrome(int x) {        if(x<0|| (x!=0 &&x%10==0)) return false;        int sum=0;        while(x>sum)        {            sum = sum*10+x%10;            x = x/10;        }        return (x==sum)||(x==sum/10);        }

性能：