leetcode 208. Implement Trie (Prefix Tree) 字典树的构造

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); */