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.

Solution:

One way is to reverse the entire number and check if it equals to the original one.

Here we only reverse half of the number and can avoid overflow case.



Code:

public class Solution {
    public boolean 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 /= 10;
        }
        return x == sum || x == sum / 10;
    }
}