def weak_common_prefix_generate(self, chapter_list):
        """
        """
        trie = Trie()
        for chapter in chapter_list:
            trie.insert_string(chapter.chapter_title)

        common_prefix_list = trie.find_common_prefix(trie.root, 10, '')
        return common_prefix_list
    def strong_common_prefix_generate(self, chapter_list):
        """
        """
        trie = Trie()
        for chapter in chapter_list:
            trie.insert_string(chapter.chapter_title)

        count = int(len(chapter_list) * 0.7) + 1
        common_prefix_list = trie.find_common_prefix(trie.root, count, '')
        return common_prefix_list