leetcode 208. 实现 Trie (前缀树)

class Trie {

    /** Initialize your data structure here. */
    private Node root;
    private int size;
    public Trie(){
        root=new Node();
        
    }

    private class Node{
        public boolean isWord;
        public TreeMap<Character,Node>next;//多叉树
        public Node(boolean isWord){
            this.isWord=isWord;
            next=new TreeMap<>();
        }
        public Node(){
            // this(false);相当于调用构造器NOde(boolen is Word)
            this.isWord=false;
            next=new TreeMap<>();
        }

    }





    
    /** 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);//走到c结点
        }
        //cur 走到了word最后一个字符，不一定是叶子结点，如panda(中pan 为一个单词)
        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) return false;
            cur=cur.next.get(c);
        }
        return cur.isWord;
    }
    
    /** 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);
 */

递归实现

class Trie {

    /** Initialize your data structure here. */
    private Node root;
    private int size;
    public Trie(){
        root=new Node();
        
    }

    private class Node{
        public boolean isWord;
        public TreeMap<Character,Node>next;//多叉树
        public Node(boolean isWord){
            this.isWord=isWord;
            next=new TreeMap<>();
        }
        public Node(){
            // this(false);相当于调用构造器NOde(boolen is Word)
            this.isWord=false;
            next=new TreeMap<>();
        }

    }





    
    /** Inserts a word into the trie. */

    public void insert(String word){
        _insert(root,0,word);
    }
    // 从cur 节点构建word[index:]求word[0:]
    public  void _insert(Node cur,int i,String word){
       if(i==word.length())
         {
             cur.isWord=true;
             return ;
         }
        //cur 走到了word最后一个字符，不一定是叶子结点，如panda(中pan 为一个单词)
        char c=word.charAt(i);
        if(cur.next.get(c)==null)
            cur.next.put(c,new Node());
        cur=cur.next.get(c);//走到c结点
        _insert(cur,i+1,word);
    
    }


    /** Returns if the word is in the trie. */

    public boolean search(String word){
       return _search(word,root,0);
    }
    public boolean _search(String word,Node cur,int i){
        if(i==word.length()) return cur.isWord;
            char c=word.charAt(i);
            if(cur.next.get(c)==null) return false;
            cur=cur.next.get(c);
         return _search(word, cur, i+1);
    }
    /** Returns if there is any word in the trie that starts with the given prefix. */

     public boolean startsWith(String prefix){
        return _startsWith(prefix,root,0);
    }
     public boolean _startsWith(String word,Node cur,int i){
        if(i==word.length()) return true;
            char c=word.charAt(i);
            if(cur.next.get(c)==null) return false;
            cur=cur.next.get(c);
        return _startsWith(word,cur,i+1);
    }
}

/**
 * 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);
 */