class Solution {
    public boolean isPalindrome(String s) {
        for(int i=0, j=s.length()-1; i<j; ){
            char chari=s.charAt(i);
            char charj=s.charAt(j);
            if(!Character.isLetterOrDigit(chari)) {
                i++; continue;
            }
            if(!Character.isLetterOrDigit(charj)) {
                j--; continue;
            }
            if(Character.isLetterOrDigit(chari) && Character.isLetterOrDigit(charj) 
               && Character.toLowerCase(chari)!=Character.toLowerCase(charj)) return false;
            else{
                i++;j--;
            }
        }
        return true;
    }
}