Problem

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

For 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.

My Solution

class Solution {
   public boolean isPalindrome(String s) {
        if (s.isEmpty()) {
            return true;
        }
        int head = 0, tail = s.length() - 1;
        char cHead, cTail;
        while (head <= tail) {
            cHead = s.charAt(head);
            cTail = s.charAt(tail);
            if (!Character.isLetterOrDigit(cHead)) {
                head++;
            } else if (!Character.isLetterOrDigit(cTail)) {
                tail--;
            } else {
                if (Character.toLowerCase(cHead) != Character.toLowerCase(cTail)) {
                    return false;
                }
                head++;
                tail--;
            }
        }
        return true;
   }
}

Great Solution

public boolean isPalindrome(String s) {
    String actual = s.replaceAll("[^A-Za-z0-9]", "").toLowerCase();
    String rev = new StringBuffer(actual).reverse().toString();
    return actual.equals(rev);
}