LeetCode:208. 实现 Trie (前缀树)

class Trie {

    private class Node{
        public boolean isWord;
        public TreeMap<Character,Node>next;

        public Node(boolean isWord){
            this.isWord=isWord;
            next=new TreeMap<>();
        }

        public Node(){
            this(false);
        }
    }

    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 cur = root;
        for(int i = 0 ; i < word.length() ; i ++){
            char c = word.charAt(i);
            if(cur.next.get(c) == null)
                cur.next.put(c, new Node());
            cur = cur.next.get(c);
        }
        if(!cur.isWord){
            cur.isWord = true;
        }
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        Node cur=root;
        for(int i=0;i<word.length();i++){
            char c=word.charAt(i);
            if(cur.next.get(c)==null){
                //当前字母中断
                return false;
            }
            cur=cur.next.get(c);//取得下一个字符
        }
        return cur.isWord;//panda 存储在字典树中的话不代表 pan 也存储在字典树种

    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        Node cur=root;
        for(int i=0;i<prefix.length();i++){
            char c=prefix.charAt(i);
            if(cur.next.get(c)==null){
                return false;
            }
            cur=cur.next.get(c);
        }
        return true;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */