Valid Palindrome

24%

Accepted

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Have you met this question in a real interview? 

Yes

Example

"A man, a plan, a canal: Panama" is a palindrome.

"race a car" is not a palindrome.

Note

Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

Challenge

O(n) time without extra memory.

public class Solution {
    /**
     * @param s A string
     * @return Whether the string is a valid palindrome
     */
    public boolean isPalindrome(String s) {
        // Write your code here
        if(s == null || s.length() == 0) return true;
        s = s.toLowerCase();
        int i = 0, j = s.length() - 1;
        while(i < j){
            if(!Character.isLetterOrDigit(s.charAt(i))) i++;
            else if(!Character.isLetterOrDigit(s.charAt(j))) j--;
            else if(s.charAt(i) != s.charAt(j)) return false;
            else{
                i++;
                j--;
            }
           
        }
        return true;
    }
}