Java实现单词树(trie)

package com.shundong.utils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/** 
 * 一个只能处理26个字母的单词树（trie)
 * 空间换时间 T(n) = O(n) 
 * ps:如果缺陷 欢迎留言
 * @author shundong
 * @data 2018-10-13
 */

public class FindWordsTrie{
	//一个Trie树有一个根节点
	private Vertex root;

	//内部类or节点类
	protected class Vertex{
		protected int words;
		protected int prefixes;
		//每个节点包含26个子节点(类型为自身)
		protected Vertex[] edges;
		Vertex() {
			words = 0;
			prefixes = 0;
			edges = new Vertex[26];
			for (int i = 0; i < edges.length; i++) {
				edges[i] = null;
			}
		}
	}

	public FindWordsTrie () {
		root = new Vertex();
	}

	/** 
	 * 列出List所有单词
	 * @return
	 */
	public List< String> listAllWords() {

		List< String> words = new ArrayList< String>();
		Vertex[] edges = root.edges;

		for (int i = 0; i < edges.length; i++) {
			if (edges[i] != null) {
				String word = "" + (char)('a' + i);
				depthFirstSearchWords(words, edges[i], word);
			}
		}        
		return words;
	}

	/** 
	 * Depth First在Trie中搜索单词并将它们添加到List中。
	 * @param words
	 * @param vertex
	 * @param wordSegment
	 */
	private void depthFirstSearchWords(List words, Vertex vertex, String wordSegment) {
		Vertex[] edges = vertex.edges;
		boolean hasChildren = false;
		for (int i = 0; i < edges.length; i++) {
			if (edges[i] != null) {
				hasChildren = true;
				String newWord = wordSegment + (char)('a' + i);                
				depthFirstSearchWords(words, edges[i], newWord);
			}            
		}
		if (!hasChildren) {
			words.add(wordSegment);
		}
	}

	public int countPrefixes(String prefix) {
		return countPrefixes(root, prefix);
	}

	private int countPrefixes(Vertex vertex, String prefixSegment) {
		if (prefixSegment.length() == 0) { //到达单词的最后一个字符
			return vertex.prefixes;
		}
		char c = prefixSegment.charAt(0);
		int index = c - 'a';
		if (vertex.edges[index] == null) { // 这个词不存在
			return 0;
		} else {
			return countPrefixes(vertex.edges[index], prefixSegment.substring(1));
		}        
	}

	public int countWords(String word) {
		return countWords(root, word);
	}    

	private int countWords(Vertex vertex, String wordSegment) {
		if (wordSegment.length() == 0) { //到达单词的最后一个字符
			return vertex.words;
		}
		char c = wordSegment.charAt(0);
		int index = c - 'a';
		if (vertex.edges[index] == null) { // 这个词不存在
			return 0;
		} else {
			return countWords(vertex.edges[index], wordSegment.substring(1));
		}        

	}
	/** 
	 * 在Trie上添加一个单词
	 * @param word 要添加的词
	 */
	public void addWord(String word) {
		addWord(root, word);
	}
	/** 
	 * 添加指定顶点的单词
	 * @param vertex 指定的顶点
	 * @param word 要添加的词
	 */
	private void addWord(Vertex vertex, String word) {
		if (word.length() == 0) { //如果已添加该单词的所有字符
			vertex.words ++;
		} else {
			vertex.prefixes ++;
			char c = word.charAt(0);
			c = Character.toLowerCase(c);
			int index = c - 'a';
			if (vertex.edges[index] == null) { //如果边缘不存在
				vertex.edges[index] = new Vertex();
			}
			addWord(vertex.edges[index], word.substring(1)); //去下一个
		}
	}
	//简单的测试测试
	public static void main(String args[])  
	{
		FindWordsTrie trie = new FindWordsTrie();
		trie.addWord("cabbage");
		trie.addWord("cabbage");
		trie.addWord("cabbage");
		trie.addWord("cabbage");
		trie.addWord("cabin");
		trie.addWord("berte");
		trie.addWord("cabbage");
		trie.addWord("english");
		trie.addWord("establish");
		trie.addWord("good");

		//				System.out.println(trie.root.prefixes);
		//				System.out.println(trie.root.words);
		//				List< String> list = trie.listAllWords();
		//				Iterator listiterator = list.listIterator();
		//				//遍历
		//				while(listiterator.hasNext())
		//				{
		//					String str = (String)listiterator.next();
		//					System.out.println(str);
		//				}
		int count = trie.countPrefixes("c");//此处传参
		int count1=trie.countWords("cabbage");
		System.err.println("单词c 前缀个数为:"+count);
		System.err.println("cabbage 单词的个数为:"+count1);
	}
}