get Difference between two String

Description

Demo Code

/*//  w  ww. jav a  2s .c om
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 com.java2s;

public class Main {
    public static double getDiff(String s1, String s2) {
        double avgLength = (s1.length() + s2.length()) / 2.0 + .1;
        int ld = getDist(s1, s2);
        return ld / avgLength;
    }

    /**
     * <p>Find the Levenshtein distance between two Strings.</p>
     *
     * <p>This is the number of changes needed to change one String into
     * another, where each change is a single character modification (deletion,
     * insertion or substitution).</p>
     *
     * <p>The previous implementation of the Levenshtein distance algorithm
     * was from <a href="http://www.merriampark.com/ld.htm">http://www.merriampark.com/ld.htm</a></p>
     *
     * <p>Chas Emerick has written an implementation in Java, which avoids an OutOfMemoryError
     * which can occur when my Java implementation is used with very large strings.<br>
     * This implementation of the Levenshtein distance algorithm
     * is from <a href="http://www.merriampark.com/ldjava.htm">http://www.merriampark.com/ldjava.htm</a></p>
     *
     * <pre>
     * StringUtils.getLevenshteinDistance(null, *)             = IllegalArgumentException
     * StringUtils.getLevenshteinDistance(*, null)             = IllegalArgumentException
     * StringUtils.getLevenshteinDistance("","")               = 0
     * StringUtils.getLevenshteinDistance("","a")              = 1
     * StringUtils.getLevenshteinDistance("aaapppp", "")       = 7
     * StringUtils.getLevenshteinDistance("frog", "fog")       = 1
     * StringUtils.getLevenshteinDistance("fly", "ant")        = 3
     * StringUtils.getLevenshteinDistance("elephant", "hippo") = 7
     * StringUtils.getLevenshteinDistance("hippo", "elephant") = 7
     * StringUtils.getLevenshteinDistance("hippo", "zzzzzzzz") = 8
     * StringUtils.getLevenshteinDistance("hello", "hallo")    = 1
     * </pre>
     *
     * @param s  the first String, must not be null
     * @param t  the second String, must not be null
     * @return result distance
     * @throws IllegalArgumentException if either String input <code>null</code>
     */
    public static int getDist(String s, String t) {
        if (s == null || t == null) {
            throw new IllegalArgumentException("Strings must not be null");
        }

        /*
           The difference between this impl. and the previous is that, rather 
           than creating and retaining a matrix of size s.length()+1 by t.length()+1, 
           we maintain two single-dimensional arrays of length s.length()+1.  The first, d,
           is the 'current working' distance array that maintains the newest distance cost
           counts as we iterate through the characters of String s.  Each time we increment
           the index of String t we are comparing, d is copied to p, the second int[].  Doing so
           allows us to retain the previous cost counts as required by the algorithm (taking 
           the minimum of the cost count to the left, up one, and diagonally up and to the left
           of the current cost count being calculated).  (Note that the arrays aren't really 
           copied anymore, just switched...this is clearly much better than cloning an array 
           or doing a System.arraycopy() each time  through the outer loop.)
                    
           Effectively, the difference between the two implementations is this one does not 
           cause an out of memory condition when calculating the LD over two very large strings.
         */

        int n = s.length(); // length of s
        int m = t.length(); // length of t

        if (n == 0) {
            return m;
        } else if (m == 0) {
            return n;
        }

        if (n > m) {
            // swap the input strings to consume less memory
            String tmp = s;
            s = t;
            t = tmp;
            n = m;
            m = t.length();
        }

        int p[] = new int[n + 1]; //'previous' cost array, horizontally
        int d[] = new int[n + 1]; // cost array, horizontally
        int _d[]; //placeholder to assist in swapping p and d

        // indexes into strings s and t
        int i; // iterates through s
        int j; // iterates through t

        char t_j; // jth character of t

        int cost; // cost

        for (i = 0; i <= n; i++) {
            p[i] = i;
        }

        for (j = 1; j <= m; j++) {
            t_j = t.charAt(j - 1);
            d[0] = j;

            for (i = 1; i <= n; i++) {
                cost = s.charAt(i - 1) == t_j ? 0 : 1;
                // minimum of cell to the left+1, to the top+1, diagonally left and up +cost
                d[i] = Math.min(Math.min(d[i - 1] + 1, p[i] + 1), p[i - 1]
                        + cost);
            }

            // copy current distance counts to 'previous row' distance counts
            _d = p;
            p = d;
            d = _d;
        }

        // our last action in the above loop was to switch d and p, so p now 
        // actually has the most recent cost counts
        return p[n];
    }
}
get Difference between two String - Java java.lang

Description

Demo Code

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