leetcode 208. Implement Trie (Prefix Tree) 字典树的构造 + 必须要掌握的数据结构

朴灿烈づ我的快乐病毒、 2022-06-08 09:14 95阅读 0赞

Implement a trie with insert, search, and startsWith methods.

Note:  
You may assume that all inputs are consist of lowercase letters a-z.

这道题考察的就是字典树的构造，本题是使用HashMap来完成构造，说实话之前没有学过字典树俄构造，这也算第一次吧，不过这个数据结构真的很棒。

**本题给我的最大的启发就是注意使用HashMap等数据结构。**

代码如下：

import java.util.HashMap;
    import java.util.Map;
    /*
     * 字典树，这个需要好好学习
     * http://blog.csdn.net/xudli/article/details/45598337
     * 记着吧
     * */
    class TrieNode
    {
        char c;
        boolean isLeaf=false;
        Map<Character, TrieNode> childred=new HashMap<Character, TrieNode>();
    
        public TrieNode(char d) 
        {
            c=d;
        }
    
        public TrieNode() 
        {
        }
    }
    
    public class Trie
    {
        
        TrieNode root=null;
        /** Initialize your data structure here. */
        public Trie() 
        {
            root=new TrieNode();
        }
    
        /** Inserts a word into the trie. */
        public void insert(String word)
        {
            Map<Character, TrieNode> childred=root.childred;
            for(int i=0;i<word.length();i++)
            {
                char c=word.charAt(i);
                TrieNode one=null;
                if(childred.containsKey(c))
                    one=childred.get(c);
                else
                {
                    one=new TrieNode(c);
                    childred.put(c, one);
                }
                childred=one.childred;
                if(i==word.length()-1)
                    one.isLeaf=true;
            }
        }
    
        /** Returns if the word is in the trie. */
        public boolean search(String word) 
        {
            TrieNode res=searchNode(word);
            if(res!=null && res.isLeaf)
                return true;
            else 
                return false;
        }
    
        /** Returns if there is any word in the trie that starts with the given prefix. */
        public boolean startsWith(String prefix) 
        {
            TrieNode res=searchNode(prefix);
            if(res!=null)
                return true;
            else 
                return false;
        }
    
    
        private TrieNode searchNode(String word) 
        {
            TrieNode res=null;
            Map<Character, TrieNode> childred=root.childred;
            for(int i=0;i<word.length();i++)
            {
                char c=word.charAt(i);
                if(childred.containsKey(c)==false)
                    return null;
                else
                {
                    res=childred.get(c);
                    childred=res.childred;
                }
            }
            return res;
        }
    }
    
    /**
     * 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);
     */