Each path of the trie represents an episode X and the corresponding frequency is recorded in the last node of the path.Moreover, the time positions of X are kept in the node.

• 我们使用字首树来精简地表示所有的频繁序列性段落，字首树上的一个路径表示一个频繁序列性段落，它出现的次数被记在对应路径的尾端节点上。