字典树 04 字典树中的前缀问题

查询是否在Trie中有单词以prefix为前缀

• prefix在Trie中都找到的情况下，不用再判断prefix.charAt(prefix.length - 1)所对应的节点是否是单词，直接返回true即可；

// 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;
}

A Problem In Leetcode

208. 实现 Trie (前缀树)

public 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;

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

    // 向Trie中添加一个新的单词word
    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);
        }
        cur.isWord = true;
    }

    // 查询单词word是否在Trie中
    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;
    }

    // 查询是否在Trie中有单词以prefix为前缀
    public boolean startsWith(String isPrefix){

        Node cur = root;
        for(int i = 0 ; i < isPrefix.length() ; i ++){
            char c = isPrefix.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);
 */