code: private static String pickDelimiter(String[] strings) {
      boolean allLength1 = true;
      for (String s : strings) {
        if (s.length() != 1) {
          allLength1 = false;
          break;
        }
      }
  
      if (allLength1) {
        return "";
      }
  
      String[] delimiters = new String[]{" ", ";", ",", "{", "}", null};
      int i = 0;
      NEXT_DELIMITER: for (; delimiters[i] != null; i++) {
        for (String cur : strings) {
          if (cur.contains(delimiters[i])) {
            continue NEXT_DELIMITER;
          }
        }
        break;
      }
      return delimiters[i];
    }
docs: Find a delimiter that does not occur in the given strings
  @param strings The strings that must be separated.
  @return a delimiter string or null