private static boolean isUniqueSymbolsInString(final String str){
    if(str == null || str.length() == 0) return true;
    if(str.length() > 256) return false;
    
    boolean[] arr = new boolean[256];
    
    for(char c : str.toCharArray()){
      int temp = (int)c;
      System.out.println(c);
      if(arr[temp]){
        return false;
      } else {
        arr[temp] = true;
      }
    }
    return true;
    
  }