LevenshteinDistance.java

/*
 * Encog(tm) Core v3.4 - Java Version
 * http://www.heatonresearch.com/encog/
 * https://github.com/encog/encog-java-core
 
 * Copyright 2008-2016 Heaton Research, Inc.
 *
 * 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.
 *   
 * For more information on Heaton Research copyrights, licenses 
 * and trademarks visit:
 * http://www.heatonresearch.com/copyright
 */
package org.encog.util.text;

/**
 * 
 * http://en.wikipedia.org/wiki/Levenshtein_distance
 */
public class LevenshteinDistance {

	public static int computeDistance(String s1, String s2) {
		s1 = s1.toLowerCase();
		s2 = s2.toLowerCase();

		final int[] costs = new int[s2.length() + 1];
		for (int i = 0; i <= s1.length(); i++) {
			int lastValue = i;
			for (int j = 0; j <= s2.length(); j++) {
				if (i == 0) {
					costs[j] = j;
				} else {
					if (j > 0) {
						int newValue = costs[j - 1];
						if (s1.charAt(i - 1) != s2.charAt(j - 1)) {
							newValue = Math.min(Math.min(newValue, lastValue),
									costs[j]) + 1;
						}
						costs[j - 1] = lastValue;
						lastValue = newValue;
					}
				}
			}
			if (i > 0) {
				costs[s2.length()] = lastValue;
			}
		}
		return costs[s2.length()];
	}
}