LeetCode 125 - Valid Palindrome

https://leetcode.com/problems/valid-palindrome/

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

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

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

https://leetcode.com/problems/valid-palindrome/discuss/40029/Accepted-pretty-Java-solution(271ms)
https://leetcode.com/problems/valid-palindrome/discuss/40048/Here's-a-clean-C%2B%2B-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;
    }

X. https://leetcode.com/problems/valid-palindrome/discuss/39981/My-three-line-java-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);
    }