ohair@286: /*
ohair@286:  * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.
ohair@286:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
ohair@286:  *
ohair@286:  * This code is free software; you can redistribute it and/or modify it
ohair@286:  * under the terms of the GNU General Public License version 2 only, as
ohair@286:  * published by the Free Software Foundation.  Oracle designates this
ohair@286:  * particular file as subject to the "Classpath" exception as provided
ohair@286:  * by Oracle in the LICENSE file that accompanied this code.
ohair@286:  *
ohair@286:  * This code is distributed in the hope that it will be useful, but WITHOUT
ohair@286:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
ohair@286:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
ohair@286:  * version 2 for more details (a copy is included in the LICENSE file that
ohair@286:  * accompanied this code).
ohair@286:  *
ohair@286:  * You should have received a copy of the GNU General Public License version
ohair@286:  * 2 along with this work; if not, write to the Free Software Foundation,
ohair@286:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
ohair@286:  *
ohair@286:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
ohair@286:  * or visit www.oracle.com if you need additional information or have any
ohair@286:  * questions.
ohair@286:  */
ohair@286: 
ohair@286: package com.sun.xml.internal.bind.v2.util;
ohair@286: 
mkos@397: import java.util.AbstractMap;
mkos@397: import java.util.Arrays;
ohair@286: import java.util.Collection;
mkos@397: import java.util.WeakHashMap;
ohair@286: 
ohair@286: /**
ohair@286:  * Computes the string edit distance.
ohair@286:  *
ohair@286:  * <p>
ohair@286:  * Refer to a computer science text book for the definition
ohair@286:  * of the "string edit distance".
ohair@286:  *
ohair@286:  * @author
ohair@286:  *     Kohsuke Kawaguchi (kohsuke.kawaguchi@sun.com)
ohair@286:  */
ohair@286: public class EditDistance {
ohair@286: 
ohair@286:     /**
mkos@397:      * Weak results cache to avoid additional computations.
mkos@397:      * Because of high complexity caching is required.
mkos@397:      */
mkos@397:     private static final WeakHashMap<AbstractMap.SimpleEntry<String,String>, Integer> CACHE = new WeakHashMap<AbstractMap.SimpleEntry<String, String>, Integer>();
mkos@397: 
mkos@397:     /**
ohair@286:      * Computes the edit distance between two strings.
ohair@286:      *
ohair@286:      * <p>
ohair@286:      * The complexity is O(nm) where n=a.length() and m=b.length().
ohair@286:      */
ohair@286:     public static int editDistance( String a, String b ) {
mkos@397:         // let's check cache
mkos@397:         AbstractMap.SimpleEntry<String,String> entry = new AbstractMap.SimpleEntry<String, String>(a, b); // using this class to avoid creation of my own which will handle PAIR of values
mkos@397:         Integer result = null;
mkos@397:         if (CACHE.containsKey(entry))
mkos@397:             result = CACHE.get(entry); // looks like we have it
mkos@397: 
mkos@397:         if (result == null) {
mkos@397:             result = new EditDistance(a, b).calc();
mkos@397:             CACHE.put(entry, result); // cache the result
mkos@397:         }
mkos@397:         return result;
ohair@286:     }
ohair@286: 
ohair@286:     /**
ohair@286:      * Finds the string in the <code>group</code> closest to
ohair@286:      * <code>key</code> and returns it.
ohair@286:      *
ohair@286:      * @return null if group.length==0.
ohair@286:      */
ohair@286:     public static String findNearest( String key, String[] group ) {
ohair@286:         return findNearest(key, Arrays.asList(group));
ohair@286:     }
ohair@286: 
ohair@286:     /**
ohair@286:      * Finds the string in the <code>group</code> closest to
ohair@286:      * <code>key</code> and returns it.
ohair@286:      *
ohair@286:      * @return null if group.length==0.
ohair@286:      */
ohair@286:     public static String findNearest( String key, Collection<String> group ) {
ohair@286:         int c = Integer.MAX_VALUE;
ohair@286:         String r = null;
ohair@286: 
ohair@286:         for (String s : group) {
ohair@286:             int ed = editDistance(key,s);
ohair@286:             if( c>ed ) {
ohair@286:                 c = ed;
ohair@286:                 r = s;
ohair@286:             }
ohair@286:         }
ohair@286:         return r;
ohair@286:     }
ohair@286: 
ohair@286:     /** cost vector. */
ohair@286:     private int[] cost;
ohair@286:     /** back buffer. */
ohair@286:     private int[] back;
ohair@286: 
ohair@286:     /** Two strings to be compared. */
ohair@286:     private final String a,b;
ohair@286: 
ohair@286:     private EditDistance( String a, String b ) {
ohair@286:         this.a=a;
ohair@286:         this.b=b;
ohair@286:         cost = new int[a.length()+1];
ohair@286:         back = new int[a.length()+1]; // back buffer
ohair@286: 
ohair@286:         for( int i=0; i<=a.length(); i++ )
ohair@286:             cost[i] = i;
ohair@286:     }
ohair@286: 
ohair@286:     /**
ohair@286:      * Swaps two buffers.
ohair@286:      */
ohair@286:     private void flip() {
ohair@286:         int[] t = cost;
ohair@286:         cost = back;
ohair@286:         back = t;
ohair@286:     }
ohair@286: 
ohair@286:     private int min(int a,int b,int c) {
ohair@286:         return Math.min(a,Math.min(b,c));
ohair@286:     }
ohair@286: 
ohair@286:     private int calc() {
ohair@286:         for( int j=0; j<b.length(); j++ ) {
ohair@286:             flip();
ohair@286:             cost[0] = j+1;
ohair@286:             for( int i=0; i<a.length(); i++ ) {
ohair@286:                 int match = (a.charAt(i)==b.charAt(j))?0:1;
ohair@286:                 cost[i+1] = min( back[i]+match, cost[i]+1, back[i+1]+1 );
ohair@286:             }
ohair@286:         }
ohair@286:         return cost[a.length()];
ohair@286:     }
ohair@286: }