class RegexTrie {

    public String toRegex() {
        StringBuilder regex = new StringBuilder();
        // starting with the root, build the regex
        toRegex(root, regex);
        // return the resulting string
        return regex.toString();
    }

    public  RegexTrie();
    public  RegexTrie(List<String> strings);
    public  RegexTrie(String... strings);

}