leetcode -- Palindrome Number

Palindrome Number

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.

public boolean isPalindrome ( int x ) {
        if ( x>= 0 && x <= 9 ){
            return true;
        }

        if ( x<0 ){
            return false;
        } else if ( x >= 10 &&  x%10 == 0 ){
            return false;
        }

        int y = x;
        int sum = 0;

        while ( x != 0 ){
            sum = 10*sum + ( x%10 );
            x = x/10;
        }

        return y == sum;
    }

First, if x is smaller than 0, x is not a palindrome.

We define a value sum, and add the values of x from low, if new sum equals to y, then x is a palindrome.