TrieStructure.java

/*
 * Copyright 2010
 * Ubiquitous Knowledge Processing (UKP) Lab
 * Technische Universität Darmstadt
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *   
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 **/

package de.tudarmstadt.ukp.dkpro.core.decompounding.trie;

import de.tudarmstadt.ukp.dkpro.core.decompounding.dictionary.Dictionary;

/**
 * A trie datastructor which also stores the number of successor for each node
 * 
 */
public class TrieStructure
{

    // Key: substring. Value: Successors
    private KeyValueNode<String, Integer> root = new KeyValueNode<String, Integer>("", 0);

    /**
     * Adds a word to the tree. Also increments the successor value for each node
     * 
     * @param aWord
     *            a word.
     */
    public void addWord(String aWord)
    {
        KeyValueNode<String, Integer> parent = root;

        for (int i = 0; i < aWord.length(); i++) {
            String subword = aWord.substring(0, i + 1);
            KeyValueNode<String, Integer> child = parent.getChild(subword);

            if (child != null) {
                if (!subword.equals(aWord)) {
                    child.setValue(child.getValue() + 1);
                }
            }
            else {
                Integer value = 1;
                if (subword.equals(aWord)) {
                    value = 0;
                }
                child = new KeyValueNode<String, Integer>(subword, value);
                parent.addChild(child);
            }

            parent = child;
        }
    }

    /**
     * Finds a node with a given string. If not found NULL is returned.
     * 
     * @param aWord
     *            a word.
     * @return a node with a given string or {@code null}.
     */
    public KeyValueNode<String, Integer> findWord(String aWord)
    {
        aWord = aWord.toLowerCase();
        KeyValueNode<String, Integer> parent = root;
        int depth = 1;

        while (parent.hasChildren()) {
            String w = aWord.substring(0, depth);
            KeyValueNode<String, Integer> child = parent.getChild(w);

            if (w.equals(aWord)) {
                return child;
            }
            else if (child != null) {
                parent = child;
                depth++;
            }
            else {
                return null;
            }
        }

        return null;
    }

    /**
     * Returns the number of successor for a node. If the node could not be found the return value
     * is 0.
     * 
     * @param aWord
     *            a word.
     * @return the number of successor for a node.
     */
    public Integer getSuccessors(String aWord)
    {
        KeyValueNode<String, Integer> node = findWord(aWord);
        if (node != null) {
            return node.getValue();
        }

        return 0;
    }

    /**
     * Creates a Trie object for a SimpleDictionary
     * 
     * @param aDict
     *            a dictionary.
     * @return the resulting trie.
     */
    public static TrieStructure createForDict(Dictionary aDict)
    {
        TrieStructure t = new TrieStructure();

        for (String word : aDict.getAll()) {
            t.addWord(word);
        }

        return t;
    }

    /**
     * Creates a Trie object for a SimpleDictionary with all words reversed
     * 
     * @param aDict
     *            a dictionary.
     * @return the resulting trie.
     */
    public static TrieStructure createForDictReverse(Dictionary aDict)
    {
        TrieStructure t = new TrieStructure();

        for (String word : aDict.getAll()) {
            t.addWord(new StringBuffer(word).reverse().toString());
        }

        return t;
    }
}