DamerauLevenshtein.java

/**
 *
 * Copyright (c) 2009-2016 Freedomotic team http://freedomotic.com
 *
 * This file is part of Freedomotic
 *
 * 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, 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
 * Freedomotic; see the file COPYING. If not, see
 * <http://www.gnu.org/licenses/>.
 */
package com.freedomotic.nlp;

/**
 *
 * @author Enrico Nicoletti
 */
public class DamerauLevenshtein {

    private String compOne;
    private String compTwo;
    private int[][] matrix;
    private Boolean calculated = false;

    public void setWordsToCompare(String a, String b) {
        calculated = false; //reset for a new calucation
        if ((a.length() > 0 || !a.isEmpty()) || (b.length() > 0 || !b.isEmpty())) {
            compOne = a;
            compTwo = b;
        }
    }

    /**
     *
     * @return
     */
    public int[][] getMatrix() {
        setupMatrix();
        return matrix;
    }

    /**
     *
     * @return
     */
    public int getSimilarity() {
        if (!calculated) {
            setupMatrix();
        }

        return matrix[compOne.length()][compTwo.length()];
    }

    private void setupMatrix() {
        int cost = -1;
        int del;
        int sub;
        int ins;

        matrix = new int[compOne.length() + 1][compTwo.length() + 1];

        for (int i = 0; i <= compOne.length(); i++) {
            matrix[i][0] = i;
        }

        for (int i = 0; i <= compTwo.length(); i++) {
            matrix[0][i] = i;
        }

        for (int i = 1; i <= compOne.length(); i++) {
            for (int j = 1; j <= compTwo.length(); j++) {
                if (compOne.charAt(i - 1) == compTwo.charAt(j - 1)) {
                    cost = 0;
                } else {
                    cost = 1;
                }

                del = matrix[i - 1][j] + 1;
                ins = matrix[i][j - 1] + 1;
                sub = matrix[i - 1][j - 1] + cost;

                matrix[i][j] = minimum(del, ins, sub);

                if ((i > 1) && (j > 1) && (compOne.charAt(i - 1) == compTwo.charAt(j - 2)) && (compOne.charAt(i - 2) == compTwo.charAt(j - 1))) {
                    matrix[i][j] = minimum(matrix[i][j], matrix[i - 2][j - 2] + cost);
                }
            }
        }

        calculated = true;
    }

    private int minimum(int d, int i, int s) {
        int m = Integer.MAX_VALUE;

        if (d < m) {
            m = d;
        }
        if (i < m) {
            m = i;
        }
        if (s < m) {
            m = s;
        }

        return m;
    }

    private int minimum(int d, int t) {
        int m = Integer.MAX_VALUE;

        if (d < m) {
            m = d;
        }
        if (t < m) {
            m = t;
        }

        return m;
    }
}