9. Palindrome Number

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.

Solution 1

13ms 31.35%

public class Solution {    public boolean isPalindrome(int x) {        if(x < 0){            return false;        }        int devide = 1;        while(x / devide >= 10){            devide *= 10;        }        while(devide > 0){            int head = x / devide;            int tail = x % 10;            if(head != tail){                return false;            }            x = x % devide / 10;            devide /= 100;        }        return true;    }}

Solution 2 Use String
18ms 13.61%

public class Solution {    public boolean isPalindrome(int x) {        String s = String.valueOf(x);        int start = 0;        int end = s.length() - 1;        while(start < end){            if(s.charAt(start) == s.charAt(end)){                start++;                end--;            }else{                return false;            }        }        return true;    }}