Palindrome Number

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

Solution:
First, compare the first and last digit. If they are not the same, it must not be a palindrome. If they are the same, chop off one digit from both ends and continue until you have no digits left, which you conclude that it must be a palindrome.

Now, getting and chopping the last digit is easy. However, getting and chopping the first digit in a generic way requires some thought.

bool isPalindrome(int x) {
    if (x < 0) return false;
    int div = 1;
    while (x / div >= 10) {
        div *= 10;
    }
    while (x != 0) {
        int l = x / div;
        int r = x % 10;
        if (l != r) return false;
        x = (x % div) / 10;
        div /= 100;
    }
    return true;
}

Complexity:

time - O(1)
space - O(1)

Links and credits:
http://discuss.leetcode.com/questions/181/palindrome-number