private static boolean isUnique(String input)
    {
        if(input==null || input.isEmpty())
            return false;
                    
        HashSet<Character> uniqueChars = new HashSet<Character>();
        char[] inputStrArray = input.toCharArray();
        
        for(char c: inputStrArray)
        {
            if(uniqueChars.contains(c))
            {
               return false; 
            }
            else
            {
                uniqueChars.add(c);
            }
        }
        
        return true;
    }