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);}
}