[125. Valid Palindrome] #leetcode

125_0914.java

class Solution {
    public boolean isPalindrome(String s) {
        if (s.length() == 0) return true;
        
        StringBuilder validLetters = new StringBuilder();
        for (Character c : s.toCharArray()) {
            if (Character.isLetter(c) || Character.isDigit(c)) {
                validLetters.append(Character.toLowerCase(c));
            }
        }

        return validLetters.toString().equals(validLetters.reverse().toString());
    }
}