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<BLOCKQUOTE>import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* A word trie which can only deal with 26 alphabeta letters.
*/
public class Trie{
private Vertex root;//一个Trie树有一个根节点
//内部类
protected class Vertex{//节点类
protected int words;
protected int prefixes;
protected Vertex[] edges;//每个节点包含26个子节点(类型为自身)
Vertex() {
words = 0;
prefixes = 0;
edges = new Vertex[26];
for (int i = 0; i < edges.length; i++) {
edges[i] = null;
}
}
}
public Trie () {
root = new Vertex();
}
/** *//**
* List all words in the Trie.
* @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 Search words in the Trie and add them to the List.
*
* @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) { //reach the last character of the word
return vertex.prefixes;
}
char c = prefixSegment.charAt(0);
int index = c - 'a';
if (vertex.edges[index] == null) { // the word does NOT exist
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) { //reach the last character of the word
return vertex.words;
}
char c = wordSegment.charAt(0);
int index = c - 'a';
if (vertex.edges[index] == null) { // the word does NOT exist
return 0;
} else {
return countWords(vertex.edges[index], wordSegment.substring(1));
}
}
/** *//**
* Add a word to the Trie.
* @param word The word to be added.
*/
public void addWord(String word) {
addWord(root, word);
}
/** *//**
* Add the word from the specified vertex.
* @param vertex The specified vertex.
* @param word The word to be added.
*/
private void addWord(Vertex vertex, String word) {
if (word.length() == 0) { //if all characters of the word has been added
vertex.words ++;
} else {
vertex.prefixes ++;
char c = word.charAt(0);
c = Character.toLowerCase(c);
int index = c - 'a';
if (vertex.edges[index] == null) { //if the edge does NOT exist
vertex.edges[index] = new Vertex();
}
addWord(vertex.edges[index], word.substring(1)); //go the the next character
}
}
public static void main(String args[]) //Just used for test
{
Trie trie = new Trie();
trie.addWord("China");
trie.addWord("China");
trie.addWord("China");
trie.addWord("crawl");
trie.addWord("crime");
trie.addWord("ban");
trie.addWord("China");
trie.addWord("english");
trie.addWord("establish");
trie.addWord("eat");
System.out.println(trie.root.prefixes);
System.out.println(trie.root.words);
List< String> list = trie.listAllWords();
Iterator listiterator = list.listIterator();
while(listiterator.hasNext())
{
String s = (String)listiterator.next();
System.out.println(s);
}
int count = trie.countPrefixes("ch");
int count1=trie.countWords("china");
System.out.println("the count of c prefixes:"+count);
System.out.println("the count of china countWords:"+count1);
}
}

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