021.实现trie树

import java.util.TreeMap;

public class Trie {//注意Trie只能存储字符串
    private class Node{
        public boolean isWord;
        public TreeMap<Character,Node>next;//父节点与子节点是通过映射来实现的，这是为了更好地扩充

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

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

    private Node root;
    private int size;

    public Trie(){
        root=new Node();
        size=0;
    }

    //获取Trie中的单词数量
    public int getSize(){
        return size;
    }

    // 向Trie中添加一个新的单词word
    public void add(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;
            size ++;
        }
    }

    //查询单词word是否在Trie中
    public boolean contains(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
    }

    //查询是否在trie中有单词以prefix为前缀
    public boolean isPrefix(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;
    }
}

public class Main {
    public static void main(String[] args) {
        //Code
        Trie obj=new Trie();
        String s="string";
        obj.add(s);
        System.out.println(obj.getSize());
        System.out.println(obj.contains("sss"));
        System.out.println(obj.contains("string"));
    }
}