Ternary Search Tree
The Ternary Search Tree (TST) is a type of trie in which nodes are arranged in a manner similar to a Binary Search Tree, but with up to three children rather than the binary tree's limit of two.
Each node of a Ternary Search Tree stores a single character from our alphabet Σ and can have three children: a middle child, left child, and right child
拜訪規則：假設要在某TST中搜尋一個字串"eat"，假設當前的node比e大，往left child移動，比e小，往right child移動，==e，找到了，則從middle child往下，並且當前字母設成a（下一個字母），重複這個步驟直到t也被找到，且該node為end of word。