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The Waikato Environment for Knowledge Analysis (WEKA), a machine
learning workbench. This is the stable version. Apart from bugfixes, this version
does not receive any other updates.
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* Trie.java
* Copyright (C) 2007 University of Waikato, Hamilton, New Zealand
*/
package weka.core;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Vector;
import javax.swing.tree.DefaultMutableTreeNode;
/**
* A class representing a Trie data structure for strings.
* See also Trie
* on WikiPedia.
*
* @author fracpete (fracpete at waikato dot ac dot nz)
* @version $Revision: 1.2 $
*/
public class Trie
implements Serializable, Cloneable, Collection, RevisionHandler {
/** for serialization */
private static final long serialVersionUID = -5897980928817779048L;
/**
* Represents a node in the trie.
*
* @author fracpete (fracpete at waikato dot ac dot nz)
* @version $Revision: 1.2 $
*/
public static class TrieNode
extends DefaultMutableTreeNode
implements RevisionHandler {
/** for serialization */
private static final long serialVersionUID = -2252907099391881148L;
/** the stop character */
public final static Character STOP = '\0';
/** for fast access to the children */
protected Hashtable m_Children;
/**
* initializes the node
*
* @param c the value of this node
*/
public TrieNode(char c) {
this(new Character(c));
}
/**
* initializes the node
*
* @param c the value of this node
*/
public TrieNode(Character c) {
super(c);
m_Children = new Hashtable(100);
}
/**
* returns the stored character
*
* @return the stored character
*/
public Character getChar() {
return (Character) getUserObject();
}
/**
* sets the character this node represents
*
* @param value the character to store
*/
public void setChar(Character value) {
setUserObject(value);
}
/**
* adds the given string to its children (creates children if necessary)
*
* @param suffix the suffix to add to its children
* @return true if the add operation changed the structure
*/
public boolean add(String suffix) {
boolean result;
Character c;
String newSuffix;
TrieNode child;
result = false;
c = suffix.charAt(0);
newSuffix = suffix.substring(1);
// find child and add if necessary
child = m_Children.get(c);
if (child == null) {
result = true;
child = add(c);
}
// propagate remaining suffix
if (newSuffix.length() > 0)
result = child.add(newSuffix) || result;
return result;
}
/**
* adds the given charater to its children
*
* @param c the character to add
* @return the generated child node
*/
protected TrieNode add(Character c) {
TrieNode child;
child = new TrieNode(c);
add(child);
m_Children.put(c, child);
return child;
}
/**
* removes the given characted from its children
*
* @param c the character to remove
*/
protected void remove(Character c) {
TrieNode child;
child = m_Children.get(c);
remove(child);
m_Children.remove(c);
}
/**
* Removes a suffix from the trie.
*
* @param suffix the suffix to remove
* @return true if this trie changed as a result of the call
*/
public boolean remove(String suffix) {
boolean result;
Character c;
String newSuffix;
TrieNode child;
c = suffix.charAt(0);
newSuffix = suffix.substring(1);
child = m_Children.get(c);
if (child == null) {
result = false;
}
else if (newSuffix.length() == 0) {
remove(c);
result = true;
}
else {
result = child.remove(newSuffix);
if (child.getChildCount() == 0)
remove(child.getChar());
}
return result;
}
/**
* checks whether a suffix can be found in its children
*
* @param suffix the suffix to look for
* @return true if suffix was found
*/
public boolean contains(String suffix) {
boolean result;
Character c;
String newSuffix;
TrieNode child;
c = suffix.charAt(0);
newSuffix = suffix.substring(1);
child = m_Children.get(c);
if (child == null)
result = false;
else if (newSuffix.length() == 0)
result = true;
else
result = child.contains(newSuffix);
return result;
}
/**
* creates a deep copy of itself
*
* @return a deep copy of itself
*/
public Object clone() {
TrieNode result;
Enumeration keys;
Character key;
TrieNode child;
result = new TrieNode(getChar());
keys = m_Children.keys();
while (keys.hasMoreElements()) {
key = keys.nextElement();
child = (TrieNode) m_Children.get(key).clone();
result.add(child);
result.m_Children.put(key, child);
}
return result;
}
/**
* Indicates whether some other object is "equal to" this one.
*
* @param obj the object to check for equality
* @return true if equal
*/
public boolean equals(Object obj) {
boolean result;
TrieNode node;
Enumeration keys;
Character key;
node = (TrieNode) obj;
// is payload the same?
if (getChar() == null)
result = (node.getChar() == null);
else
result = getChar().equals(node.getChar());
// check children
if (result) {
keys = m_Children.keys();
while (keys.hasMoreElements()) {
key = keys.nextElement();
result = m_Children.get(key).equals(node.m_Children.get(key));
if (!result)
break;
}
}
return result;
}
/**
* returns the node with the given suffix
*
* @param suffix the suffix to look for
* @return null if unsuccessful otherwise the corresponding node
*/
public TrieNode find(String suffix) {
TrieNode result;
Character c;
String newSuffix;
TrieNode child;
c = suffix.charAt(0);
newSuffix = suffix.substring(1);
child = m_Children.get(c);
if (child == null)
result = null;
else if (newSuffix.length() == 0)
result = child;
else
result = child.find(newSuffix);
return result;
}
/**
* returns the common prefix for all the nodes starting with this node.
* The result includes this node, unless it's the root node or a STOP node.
*
* @return the result of the search
*/
public String getCommonPrefix() {
return getCommonPrefix("");
}
/**
* returns the common prefix for all the nodes starting with the node
* for the specified prefix. Can be null if initial prefix is not found.
* The result includes this node, unless it's the root node or a STOP node.
* Using the empty string means starting with this node.
*
* @param startPrefix the prefix of the node to start the search from
* @return the result of the search, null if startPrefix
* cannot be found
*/
public String getCommonPrefix(String startPrefix) {
String result;
TrieNode startNode;
if (startPrefix.length() == 0)
startNode = this;
else
startNode = find(startPrefix);
if (startNode == null)
result = null;
else
result = startPrefix + startNode.determineCommonPrefix("");
return result;
}
/**
* determines the common prefix of the nodes.
*
* @param currentPrefix the common prefix found so far
* @return the result of the search
*/
protected String determineCommonPrefix(String currentPrefix) {
String result;
String newPrefix;
if (!isRoot() && (getChar() != STOP))
newPrefix = currentPrefix + getChar();
else
newPrefix = currentPrefix;
if (m_Children.size() == 1)
result = ((TrieNode) getChildAt(0)).determineCommonPrefix(newPrefix);
else
result = newPrefix;
return result;
}
/**
* returns the number of stored strings, i.e., leaves
*
* @return the number of stored strings
*/
public int size() {
int result;
TrieNode leaf;
result = 0;
leaf = (TrieNode) getFirstLeaf();
while (leaf != null) {
if (leaf != getRoot())
result++;
leaf = (TrieNode) leaf.getNextLeaf();
}
return result;
}
/**
* returns the full string up to the root
*
* @return the full string to the root
*/
public String getString() {
char[] result;
TrieNode node;
result = new char[this.getLevel()];
node = this;
while (node.getParent() != null) {
if (node.isRoot())
break;
else
result[node.getLevel() - 1] = node.getChar();
node = (TrieNode) node.getParent();
}
return new String(result);
}
/**
* returns the node in a string representation
*
* @return the node as string
*/
public String toString() {
return "" + getChar();
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.2 $");
}
}
/**
* Represents an iterator over a trie
*
* @author fracpete (fracpete at waikato dot ac dot nz)
* @version $Revision: 1.2 $
*/
public static class TrieIterator
implements Iterator, RevisionHandler {
/** the node to use as root */
protected TrieNode m_Root;
/** the last leaf for this root node */
protected TrieNode m_LastLeaf;
/** the current leaf node */
protected TrieNode m_CurrentLeaf;
/**
* initializes the iterator
*
* @param node the node to use as root
*/
public TrieIterator(TrieNode node) {
super();
m_Root = node;
m_CurrentLeaf = (TrieNode) m_Root.getFirstLeaf();
m_LastLeaf = (TrieNode) m_Root.getLastLeaf();
}
/**
* Returns true if the iteration has more elements.
*
* @return true if there is at least one more element
*/
public boolean hasNext() {
return (m_CurrentLeaf != null);
}
/**
* Returns the next element in the iteration.
*
* @return the next element
*/
public String next() {
String result;
result = m_CurrentLeaf.getString();
result = result.substring(0, result.length() - 1); // remove STOP
if (m_CurrentLeaf != m_LastLeaf)
m_CurrentLeaf = (TrieNode) m_CurrentLeaf.getNextLeaf();
else
m_CurrentLeaf = null;
return result;
}
/**
* ignored
*/
public void remove() {
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.2 $");
}
}
/** the root node */
protected TrieNode m_Root;
/** the hash code */
protected int m_HashCode;
/** whether the structure got modified and the hash code needs to be
* re-calculated */
protected boolean m_RecalcHashCode;
/**
* initializes the data structure
*/
public Trie() {
super();
m_Root = new TrieNode(null);
m_RecalcHashCode = true;
}
/**
* Ensures that this collection contains the specified element.
*
* @param o the string to add
* @return true if the structure changed
*/
public boolean add(String o) {
return m_Root.add(o + TrieNode.STOP);
}
/**
* Adds all of the elements in the specified collection to this collection
*
* @param c the collection to add
*/
public boolean addAll(Collection c) {
boolean result;
Iterator iter;
result = false;
iter = (Iterator) c.iterator();
while (iter.hasNext())
result = add(iter.next()) || result;
return result;
}
/**
* Removes all of the elements from this collection
*/
public void clear() {
m_Root.removeAllChildren();
m_RecalcHashCode = true;
}
/**
* returns a deep copy of itself
*
* @return a copy of itself
*/
public Object clone() {
Trie result;
result = new Trie();
result.m_Root = (TrieNode) m_Root.clone();
return result;
}
/**
* Returns true if this collection contains the specified element.
*
* @param o the object to check for in trie
* @return true if found
*/
public boolean contains(Object o) {
return m_Root.contains(((String) o) + TrieNode.STOP);
}
/**
* Returns true if this collection contains all of the elements in the
* specified collection.
*
* @param c the collection to look for in the trie
* @return true if all elements were found
*/
public boolean containsAll(Collection c) {
boolean result;
Iterator iter;
result = true;
iter = c.iterator();
while (iter.hasNext()) {
if (!contains(iter.next())) {
result = false;
break;
}
}
return result;
}
/**
* checks whether the given prefix is stored in the trie
*
* @param prefix the prefix to check
* @return true if the prefix is part of the trie
*/
public boolean containsPrefix(String prefix) {
return m_Root.contains(prefix);
}
/**
* Compares the specified object with this collection for equality.
*
* @param o the object to check for equality
*/
public boolean equals(Object o) {
return m_Root.equals(((Trie) o).getRoot());
}
/**
* returns the common prefix for all the nodes
*
* @return the result of the search
*/
public String getCommonPrefix() {
return m_Root.getCommonPrefix();
}
/**
* returns the root node of the trie
*
* @return the root node
*/
public TrieNode getRoot() {
return m_Root;
}
/**
* returns all stored strings that match the given prefix
*
* @param prefix the prefix that all strings must have
* @return all strings that match the prefix
*/
public Vector getWithPrefix(String prefix) {
Vector result;
TrieNode node;
TrieIterator iter;
result = new Vector();
if (containsPrefix(prefix)) {
node = m_Root.find(prefix);
iter = new TrieIterator(node);
while (iter.hasNext())
result.add(iter.next());
}
return result;
}
/**
* Returns the hash code value for this collection.
*
* @return the hash code
*/
public int hashCode() {
if (m_RecalcHashCode) {
m_HashCode = toString().hashCode();
m_RecalcHashCode = false;
}
return m_HashCode;
}
/**
* Returns true if this collection contains no elements.
*
* @return true if empty
*/
public boolean isEmpty() {
return (m_Root.getChildCount() == 0);
}
/**
* Returns an iterator over the elements in this collection.
*
* @return returns an iterator over all the stored strings
*/
public Iterator iterator() {
return new TrieIterator(m_Root);
}
/**
* Removes a single instance of the specified element from this collection,
* if it is present.
*
* @param o the object to remove
* @return true if this collection changed as a result of the call
*/
public boolean remove(Object o) {
boolean result;
result = m_Root.remove(((String) o) + TrieNode.STOP);
m_RecalcHashCode = result;
return result;
}
/**
* Removes all this collection's elements that are also contained in the
* specified collection
*
* @param c the collection to remove
* @return true if the collection changed
*/
public boolean removeAll(Collection c) {
boolean result;
Iterator iter;
result = false;
iter = c.iterator();
while (iter.hasNext()) {
result = remove(iter.next()) || result;
}
m_RecalcHashCode = result;
return result;
}
/**
* Retains only the elements in this collection that are contained in
* the specified collection
*
* @param c the collection to use as reference
* @return true if this collection changed as a result of the call
*/
public boolean retainAll(Collection c) {
boolean result;
Iterator iter;
Object o;
result = false;
iter = iterator();
while (iter.hasNext()) {
o = iter.next();
if (!c.contains(o))
result = remove(o) || result;
}
m_RecalcHashCode = result;
return result;
}
/**
* Returns the number of elements in this collection.
*
* @return the number of nodes in the tree
*/
public int size() {
return m_Root.size();
}
/**
* Returns an array containing all of the elements in this collection.
*
* @return the stored strings as array
*/
public Object[] toArray() {
return toArray(new String[0]);
}
/**
* Returns an array containing all of the elements in this collection; the
* runtime type of the returned array is that of the specified array.
*
* @param a the array into which the elements of this collection
* are to be stored
* @return an array containing the elements of this collection
*/
public T[] toArray(T[] a) {
Object[] result;
Iterator iter;
Vector list;
int i;
list = new Vector();
iter = iterator();
while (iter.hasNext())
list.add(iter.next());
if (Array.getLength(a) != list.size())
result = (Object[]) Array.newInstance(a.getClass().getComponentType(), list.size());
else
result = a;
for (i = 0; i < list.size(); i++)
result[i] = list.get(i);
return (T[]) result;
}
/**
* returns the node as String
*
* @param node the node to turn into a string
* @return the node as string
*/
protected String toString(TrieNode node) {
StringBuffer result;
int i;
StringBuffer indentation;
result = new StringBuffer();
// indent the node
indentation = new StringBuffer();
for (i = 0; i < node.getLevel(); i++)
indentation.append(" | ");
result.append(indentation.toString());
// add the node label
if (node.getChar() == null)
result.append("");
else if (node.getChar() == TrieNode.STOP)
result.append("STOP");
else
result.append("'" + node.getChar() + "'");
result.append("\n");
// add the children
for (i = 0; i < node.getChildCount(); i++)
result.append(toString((TrieNode) node.getChildAt(i)));
return result.toString();
}
/**
* returns the trie in string representation
*
* @return the trie as string
*/
public String toString() {
return toString(m_Root);
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.2 $");
}
/**
* Only for testing (prints the built Trie). Arguments are added to the Trie.
* If not arguments provided then a few default strings are uses for building.
*
* @param args commandline arguments
*/
public static void main(String[] args) {
String[] data;
if (args.length == 0) {
data = new String[3];
data[0] = "this is a test";
data[1] = "this is another test";
data[2] = "and something else";
}
else {
data = args.clone();
}
// build trie
Trie t = new Trie();
for (int i = 0; i < data.length; i++)
t.add(data[i]);
System.out.println(t);
}
}
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