字典树——入门学习

Posted 2022-03-02 小乖乖的臭坏坏

Trie.java

public class Trie 
    class TrieNode
        boolean isWord = false;
        TrieNode[] children; // HashMap<Character, TrieNode> children

        public TrieNode() 
            children = new TrieNode[26];
        
    

    TrieNode root;

    public Trie()
        root = new TrieNode();
    

    public void insert(String word)
        TrieNode curr = root;
        for (int i=0;i<word.length();i++)
            char c = word.charAt(i);
            int index = c - 'a';
            if(curr.children[index]==null)//curr.children.get(c) == null
                curr.children[index] = new TrieNode();
            
            curr = curr.children[index]; //curr == curr.children.get(c)
        
        curr.isWord = true;
    

    public boolean search(String word)
        TrieNode curr = root;
        for (int i=0;i<word.length();i++)
            char c = word.charAt(i);
            int index = c - 'a';
            if(curr.children[index]==null)
                return false;
            
            curr = curr.children[index];
        
        return curr.isWord;
    

    public boolean startsWith(String prefix)
        TrieNode curr = root;
        for (int i=0;i<prefix.length();i++)
            char c = prefix.charAt(i);
            int index = c - 'a';
            if(curr.children[index]==null)
                return false;
            
            curr = curr.children[index];
        
        return true;
    

TrieDemo.java

import java.util.Scanner;

public class TrieDemo 
    public static void main(String[] args) 
        Scanner cin = new Scanner(System.in);
        Trie trie = new Trie();
        String s;
        while (true)
            s = cin.nextLine();
            if (s.equals("over"))
                break;
            
            else
                String st[] = s.split(" ");
                if(st[0].equals("insert"))
                    trie.insert(st[1]);
                
                else if(st[0].equals("search"))
                    if (trie.search(st[1]))
                        System.out.println("true");
                    
                    else 
                        System.out.println("false");
                    
                
                else if (st[0].equals("startsWith"))
                    if (trie.startsWith(st[1]))
                        System.out.println("true");
                    
                    else 
                        System.out.println("false");
                    
                
            
        
    

输入：

insert apple
search apple
search app
startsWith app
insert app
search app

输出：

true
false
true
true

参考:
Leetcode 208 实现Trie(前缀树)