009 Palindrome Number [Leetcode]

题目内容：

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.

解题思路：

加入对负数的判断，并观察头尾数字是否相同。

代码如下：

class Solution {
public:
bool isPalindrome(int x) {
if(x < 0)
return false;

int digit(0);
int temp(x), front(x), back(0);
while(temp!=0) {
temp /= 10;
++digit;
}

for(int i = 0; i != digit/2; ++i) {
back *= 10;
temp = front % 10;
back += temp;
front /= 10;
}
if(digit&1 == 1)
front /= 10;

return (front==back);
}
};