adding CDDL-licensed EditDistance code (that I wrote for JAXB)

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@1160 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/util/EditDistance.java

+/*
+ * The contents of this file are subject to the terms
+ * of the Common Development and Distribution License
+ * (the "License").  You may not use this file except
+ * in compliance with the License.
+ *
+ * You can obtain a copy of the license at
+ * https://jwsdp.dev.java.net/CDDLv1.0.html
+ * See the License for the specific language governing
+ * permissions and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL
+ * HEADER in each file and include the License file at
+ * https://jwsdp.dev.java.net/CDDLv1.0.html  If applicable,
+ * add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your
+ * own identifying information: Portions Copyright [yyyy]
+ * [name of copyright owner]
+ */
+package hudson.util;
+
+/**
+ * Computes the string edit distance.
+ *
+ * <p>
+ * Refer to a computer science text book for the definition
+ * of the "string edit distance".
+ *
+ * @author
+ *     Kohsuke Kawaguchi (kohsuke.kawaguchi@sun.com)
+ */
+public class EditDistance {
+
+    /**
+     * Computes the edit distance between two strings.
+     *
+     * <p>
+     * The complexity is O(nm) where n=a.length() and m=b.length().
+     */
+    public static int editDistance( String a, String b ) {
+        return new EditDistance(a,b).calc();
+    }
+
+    /**
+     * Finds the string in the <code>group</code> closest to
+     * <code>key</code> and returns it.
+     *
+     * @return null if group.length==0.
+     */
+    public static String findNearest( String key, String[] group ) {
+        int c = Integer.MAX_VALUE;
+        String r = null;
+
+        for (String g : group) {
+            int ed = editDistance(key, g);
+            if (c > ed) {
+                c = ed;
+                r = g;
+            }
+        }
+        return r;
+    }
+
+    /** cost vector. */
+    private int[] cost;
+    /** back buffer. */
+    private int[] back;
+
+    /** Two strings to be compared. */
+    private final String a,b;
+
+    private EditDistance( String a, String b ) {
+        this.a=a;
+        this.b=b;
+        cost = new int[a.length()+1];
+        back = new int[a.length()+1]; // back buffer
+
+        for( int i=0; i<=a.length(); i++ )
+            cost[i] = i;
+    }
+
+    /**
+     * Swaps two buffers.
+     */
+    private void flip() {
+        int[] t = cost;
+        cost = back;
+        back = t;
+    }
+
+    private int min(int a,int b,int c) {
+        return Math.min(a,Math.min(b,c));
+    }
+
+    private int calc() {
+        for( int j=0; j<b.length(); j++ ) {
+            flip();
+            cost[0] = j+1;
+            for( int i=0; i<a.length(); i++ ) {
+                int match = (a.charAt(i)==b.charAt(j))?0:1;
+                cost[i+1] = min( back[i]+match, cost[i]+1, back[i+1]+1 );
+            }
+        }
+        return cost[a.length()];
+    }
+}