/** @param parts an ArrayList of string parts that are valid in the master string
   *         Precondition: parts.size() > 0
   *  @return the string obtained by concatenating the parts of the master string
   */
  public String decodeString(ArrayList<StringPart> parts)
  {
    String word = "";
    for (StringPart p : parts)
    {
      int start = p.getStart();
      word += masterString.substring(start, start + p.getLength());
    }
    return word;
  }

  /** @param word the string to be encoded
   *         Precondition: all of the characters in word appear in the master string;
   *                       word.length() > 0
   *  @return an ArrayList of string parts of the master string that can be combined
   *          to create word
   */
  public ArrayList<StringPart> encodeString(String word)
  {
    ArrayList<StringPart> parts = new ArrayList<StringPart>();

    while (word.length() > 0)
    {
      StringPart p = findPart(word);
      parts.add(p);
      word = word.substring(p.getLength()); 1
    }
    return parts;
  }

1. Chop off the processed substring from the beginning of word.