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