Palindrome Number

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

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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:

对比第一位和最后一位，如果不同则返回false；相同，则去除第一位和最后一位，继续对比，直到0为止。

Run time complexity is O(n), constant space.

public class Solution {
    public boolean isPalindrome(int x) {
        if(x < 0)
            return false;
        if(x < 10 && x >= 0)
            return true;
        
        int div = 1;
        while(div <= x / 10) {
            div *= 10;
        }
        
        while(x != 0) {
            if(x / div != x % 10) {  //if first digit != last digit, return false
                return false;
            }
            x = (x % div) / 10;  //get rid of first digit and last digit
            div /= 100;
        }
        
        return true;
    }
}