前缀树Trie

前缀树又称字典树，通过树形结构存储单词，适用于判断单词及其前缀是否存在。具体介绍参见leetcode 208：https://leetcode-cn.com/problems/implement-trie-prefix-tree/

class Trie {
    class Node {
        Node[] list;
        boolean isEnd;
        public Node() {
            list = new Node[26];
        }

        public boolean contains(char c) {
            return list[c - 'a'] != null;
        }

        public void put(char c) {
            if (list[c - 'a'] == null)
                list[c - 'a'] = new Node();
        }

        public Node get(char c) {
            return list[c - 'a'];
        }

        public void setIsEnd() {
            this.isEnd = true;
        }

        public boolean isEnd() {
            return isEnd;
        }
    }

    private Node root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new Node();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        Node node = root;
        for (int i=0; i