/**
 *#########################################################################
 *
 * A component of the Gatherer application, part of the Greenstone digital
 * library suite from the New Zealand Digital Library Project at the
 * University of Waikato, New Zealand.
 *
 * <BR><BR>
 *
 * Author: John Thompson, Greenstone Digital Library, University of Waikato
 *
 * <BR><BR>
 *
 * Copyright (C) 1999 New Zealand Digital Library Project
 *
 * <BR><BR>
 *
 * 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.
 *
 * <BR><BR>
 *
 * 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.
 *
 * <BR><BR>
 *
 * 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.
 *########################################################################
 */

 




/* GPL_HEADER */
package org.greenstone.gatherer.util;
/**************************************************************************************
 * Title:        Gatherer
 * Description:  The Gatherer: a tool for gathering and enriching a digital collection.
 * Company:      The University of Waikato
 * Written:      28/08/02
 * Revised:      
 * @author John Thompson, 9826509
 * @author Michael Gilleland, Merriam Park Software
 * @version 2.3
 **************************************************************************************/
/** Determines the MED between two metadata element names.<BR>
 * Adapted from code by Michael Gilleland, Merriam Park Software, as detailed in a short essay called "Levenshtein Distance, in Three Flavors" available at http://www.merriampark.com/ld.htm.
 */
public class MED {
	 //****************************
	 // Get minimum of three values
	 //****************************
	 static private int Minimum (int a, int b, int c) {
		  int mi = a;
		  if (b < mi) {
				mi = b;
		  }
		  if (c < mi) {
				mi = c;
		  }
		  return mi;
	 }
	 //*****************************
	 // Compute Levenshtein distance
	 //*****************************
	 static public int LD (String s, String t) {
		  int d[][]; // matrix
		  int n; // length of s
		  int m; // length of t
		  int i; // iterates through s
		  int j; // iterates through t
		  char s_i; // ith character of s
		  char t_j; // jth character of t
		  int cost; // cost
		  // Step 1
		  // Set n to be the length of s.
		  // Set m to be the length of t.
		  // If n = 0, return m and exit.
		  // If m = 0, return n and exit.
		  // Construct a matrix containing 0..m rows and 0..n columns.
		  n = s.length ();
		  m = t.length ();
		  if (n == 0) {
				return m;
		  }
		  if (m == 0) {
				return n;
		  }
		  d = new int[n+1][m+1];
		  // Step 2
		  // Initialize the first row to 0..n.
		  // Initialize the first column to 0..m.
		  for (i = 0; i <= n; i++) {
				d[i][0] = i;
		  }
		  for (j = 0; j <= m; j++) {
				d[0][j] = j;
		  }
		  // Step 3
		  // Examine each character of s (i from 1 to n).
		  for (i = 1; i <= n; i++) {
				s_i = s.charAt (i - 1);
				// Step 4
				// Examine each character of t (j from 1 to m).
				for (j = 1; j <= m; j++) {
					 t_j = t.charAt (j - 1);
					 // Step 5
					 // If s[i] equals t[j], the cost is 0.
					 // If s[i] doesn't equal t[j], the cost is 1.
					 if (s_i == t_j) {
						  cost = 0;
					 }
					 else {
						  cost = 1;
					 }
					 // Step 6
					 // Set cell d[i,j] of the matrix equal to the minimum of:
					 // a. The cell immediately above plus 1: d[i-1,j] + 1.
					 // b. The cell immediately to the left plus 1: d[i,j-1] + 1.
					 // c. The cell diagonally above and to the left plus the cost: d[i-1,j-1] + cost.
					 d[i][j] = Minimum (d[i-1][j]+1, d[i][j-1]+1, d[i-1][j-1] + cost);
				}
		  }
		  // Step 7
		  // After the iteration steps (3, 4, 5, 6) are complete, the distance is found in cell d[n,m].
		  int result = d[n][m];
		  d = null;
		  return result;
	 }
}