[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.

这道题是判断一个数字是否构成回文，题目难度为Easy。

可以用log10(x)来计算出数字的长度，然后按位比对前后两部分来判断数字是否构成回文，具体代码：

class Solution {public:    bool isPalindrome(int x) {        if(x < 0) return false;        int len = log10(x) + 1;        for(int i=0; i<len/2; ++i) {            if((int)(x/pow(10,i))%10 != (int)(x/pow(10, len-i-1))%10)                return false;        }        return true;    }};

看了下别人的代码，大家更普遍的方法是生成倒序数字，然后判断是否和初始数字相等，具体代码：

class Solution {public:    bool isPalindrome(int x) {        int palindromeX = 0;        int inputX = x;        while(x > 0){            palindromeX = palindromeX * 10 + (x % 10);            x = x / 10;        }        return palindromeX == inputX;     }};