Valid Palindrome

    public boolean isPalindrome(String s) {        // Start typing your Java solution below        // DO NOT write main() function        int n = s.length();        if(n == 0) return true;        int start = 0;        int end = n - 1;        while(start < end) {            while(start < end && !isChar(s.charAt(start))) start++;            while(start < end && !isChar(s.charAt(end))) end--;            if(s.charAt(start) != s.charAt(end) && Math.abs(s.charAt(start) - s.charAt(end)) != 32) return false;            start++;            end--;        }        return true;    }        public boolean isChar(char c) {        if((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')) return true;        return false;    }