com.espertech.esper.util.LevenshteinDistance Maven / Gradle / Ivy

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Complex event processing and event series analysis component

There is a newer version: 7.1.0

/*
 * *************************************************************************************
 *  Copyright (C) 2006-2015 EsperTech, Inc. All rights reserved.                       *
 *  http://www.espertech.com/esper                                                     *
 *  http://www.espertech.com                                                           *
 *  ---------------------------------------------------------------------------------- *
 *  The software in this package is published under the terms of the GPL license       *
 *  a copy of which has been included with this distribution in the license.txt file.  *
 * *************************************************************************************
 */

package com.espertech.esper.util;

/**
 * Utility for string comparison based on the Levenshtein algo. 
 */
public class LevenshteinDistance
{
    /**
     * Make 3 characters an acceptable distance for reporting.
     */
    public final static int ACCEPTABLE_DISTANCE = 3;

    /**
     * Compute the distance between two strins using the Levenshtein algorithm,
     * including a case-insensitive string comparison.
     * @param str1 first string
     * @param str2 second string
     * @return distance or zero if case-insensitive string comparison found equal strings
     * or Integer.MAX_VALUE for invalid comparison because of null values.
     */
    public static int computeLevenshteinDistance(CharSequence str1, CharSequence str2)
    {
        if ((str1 == null) || (str2 == null))
        {
            return Integer.MAX_VALUE;
        }
        if (str1.toString().toLowerCase().equals(str2.toString().toLowerCase()))
        {
            return 0;
        }
        
        int[][] distance = new int[str1.length() + 1][str2.length() + 1];

        for (int i = 0; i <= str1.length(); i++)
        {
            distance[i][0] = i;
        }
        for (int j = 0; j <= str2.length(); j++)
        {
            distance[0][j] = j;
        }

        for (int i = 1; i <= str1.length(); i++)
        {
            for (int j = 1; j <= str2.length(); j++)
            {
                distance[i][j] = minimum(
                        distance[i - 1][j] + 1,
                        distance[i][j - 1] + 1,
                        distance[i - 1][j - 1]
                                + ((str1.charAt(i - 1) == str2.charAt(j - 1)) ? 0
                                : 1));
            }
        }

        return distance[str1.length()][str2.length()];
    }

    private static int minimum(int a, int b, int c)
    {
        return Math.min(Math.min(a, b), c);
    }
}