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From simonetrip...@apache.org
Subject svn commit: r1143237 - in /commons/sandbox/graph/trunk/src: main/java/org/apache/commons/graph/spanning/ test/java/org/apache/commons/graph/spanning/
Date Wed, 06 Jul 2011 01:18:26 GMT
Author: simonetripodi
Date: Wed Jul  6 01:18:25 2011
New Revision: 1143237

URL: http://svn.apache.org/viewvc?rev=1143237&view=rev
Log:
added Kruskal's algorithm implementation, optimized by a simple DisjointSet (find-union) implementation
as described on wikipedia [http://en.wikipedia.org/wiki/Disjoint-set_data_structure]

Added:
    commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSet.java
  (with props)
    commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSetNode.java
  (with props)
    commons/sandbox/graph/trunk/src/test/java/org/apache/commons/graph/spanning/KruskalTestCase.java
  (with props)
Modified:
    commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/Kruskal.java

Added: commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSet.java
URL: http://svn.apache.org/viewvc/commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSet.java?rev=1143237&view=auto
==============================================================================
--- commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSet.java
(added)
+++ commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSet.java
Wed Jul  6 01:18:25 2011
@@ -0,0 +1,117 @@
+package org.apache.commons.graph.spanning;
+
+/*
+ * 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.
+ */
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.commons.graph.Vertex;
+
+/**
+ * Simple <a href="http://en.wikipedia.org/wiki/Disjoint-set_data_structure">Disjoint-set</a>
implementation.
+ *
+ * @param <V> the Graph vertices type.
+ */
+final class DisjointSet<V extends Vertex>
+{
+
+    private final Map<V, DisjointSetNode<V>> disjointSets = new HashMap<V,
DisjointSetNode<V>>();
+
+    /**
+     * Performs the find applying the <i>path compression</i>.
+     *
+     * @param vertex
+     * @return
+     */
+    public V find( V vertex )
+    {
+        DisjointSetNode<V> vertexNode = find( getNode( vertex ) );
+
+        if ( vertexNode == vertexNode.getParent() )
+        {
+            return vertexNode.getVertex();
+        }
+
+        vertexNode.setParent( find( vertexNode.getParent() ) );
+
+        return vertexNode.getParent().getVertex();
+    }
+
+    /**
+     * Performs the find applying the <i>path compression</i>.
+     *
+     * @param node
+     * @return
+     */
+    private DisjointSetNode<V> find( DisjointSetNode<V> node )
+    {
+        if ( node == node.getParent() )
+        {
+            return node;
+        }
+        return find( node.getParent() );
+    }
+
+    /**
+     * Performs the merge by applying the <i>union by rank</i>.
+     *
+     * @param u
+     * @param v
+     */
+    public void union( V u, V v )
+    {
+        DisjointSetNode<V> uRoot = find( getNode( u ) );
+        DisjointSetNode<V> vRoot = find( getNode( v ) );
+
+        if ( uRoot == vRoot )
+        {
+            return;
+        }
+
+        int comparison = uRoot.compareTo( vRoot );
+        if ( comparison < 0 )
+        {
+            uRoot.setParent( vRoot );
+        }
+        else if ( comparison > 0 )
+        {
+            vRoot.setParent( uRoot );
+        }
+        else
+        {
+            vRoot.setParent( uRoot );
+            uRoot.increaseRank();
+        }
+    }
+
+    private DisjointSetNode<V> getNode( V vertex )
+    {
+        DisjointSetNode<V> node = disjointSets.get( vertex );
+
+        if ( node == null )
+        {
+            node = new DisjointSetNode<V>( vertex );
+            disjointSets.put( vertex, node );
+        }
+
+        return node;
+    }
+
+}

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Added: commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSetNode.java
URL: http://svn.apache.org/viewvc/commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSetNode.java?rev=1143237&view=auto
==============================================================================
--- commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSetNode.java
(added)
+++ commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/DisjointSetNode.java
Wed Jul  6 01:18:25 2011
@@ -0,0 +1,87 @@
+package org.apache.commons.graph.spanning;
+
+/*
+ * 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.
+ */
+
+import org.apache.commons.graph.Vertex;
+
+/**
+ * The {@link DisjointSet} internal node representation.
+ *
+ * @param <V> the Graph vertices type.
+ */
+final class DisjointSetNode<V extends Vertex>
+    implements Comparable<DisjointSetNode<V>>
+{
+
+    private final V vertex;
+
+    private DisjointSetNode<V> parent = this;
+
+    private Integer rank = 0;
+
+    /**
+     * 
+     *
+     * @param vertex
+     */
+    public DisjointSetNode( V vertex )
+    {
+        this.vertex = vertex;
+    }
+
+    public V getVertex()
+    {
+        return vertex;
+    }
+
+    public DisjointSetNode<V> getParent()
+    {
+        return parent;
+    }
+
+    public void setParent( DisjointSetNode<V> parent )
+    {
+        this.parent = parent;
+    }
+
+    public Integer getRank()
+    {
+        return rank;
+    }
+
+    public void increaseRank()
+    {
+        rank++;
+    }
+
+    public void setRank( int rank )
+    {
+        this.rank = rank;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public int compareTo( DisjointSetNode<V> o )
+    {
+        return rank.compareTo( o.getRank() );
+    }
+
+}

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Modified: commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/Kruskal.java
URL: http://svn.apache.org/viewvc/commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/Kruskal.java?rev=1143237&r1=1143236&r2=1143237&view=diff
==============================================================================
--- commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/Kruskal.java
(original)
+++ commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/spanning/Kruskal.java
Wed Jul  6 01:18:25 2011
@@ -19,10 +19,16 @@ package org.apache.commons.graph.spannin
  * under the License.
  */
 
-import org.apache.commons.graph.Graph;
+import java.util.HashSet;
+import java.util.PriorityQueue;
+import java.util.Set;
+
+import org.apache.commons.graph.SpanningTree;
 import org.apache.commons.graph.Vertex;
+import org.apache.commons.graph.VertexPair;
 import org.apache.commons.graph.WeightedEdge;
 import org.apache.commons.graph.WeightedGraph;
+import org.apache.commons.graph.model.MutableSpanningTree;
 
 /**
  * Kruskal's algorithm is an algorithm in graph theory that finds a minimum spanning tree
@@ -39,9 +45,46 @@ public final class Kruskal
      * @param graph the Graph for which minimum spanning tree (or forest) has to be calculated.
      * @return  the minimum spanning tree (or forest) of the input Graph.
      */
-    public static <V extends Vertex, WE extends WeightedEdge> Graph<V, WE> minimumSpanningTree(
WeightedGraph<V, WE> graph )
+    public static <V extends Vertex, WE extends WeightedEdge> SpanningTree<V, WE>
minimumSpanningTree( WeightedGraph<V, WE> graph )
     {
-        return null;
+        final Set<V> settledNodes = new HashSet<V>();
+
+        final PriorityQueue<WE> orderedEdges = new PriorityQueue<WE>( graph.getSize()
);
+
+        for ( WE edge : graph.getEdges() )
+        {
+            orderedEdges.add( edge );
+        }
+
+        final DisjointSet<V> disjointSet = new DisjointSet<V>();
+
+        MutableSpanningTree<V, WE> spanningTree = new MutableSpanningTree<V, WE>();
+
+        while ( settledNodes.size() < graph.getOrder() )
+        {
+            WE edge = orderedEdges.poll();
+
+            VertexPair<V> vertices = graph.getVertices( edge );
+            V head = vertices.getHead();
+            V tail = vertices.getTail();
+
+            if ( settledNodes.add( head ) )
+            {
+                spanningTree.addVertex( head );
+            }
+            if ( settledNodes.add( tail ) )
+            {
+                spanningTree.addVertex( tail );
+            }
+
+            if ( !disjointSet.find( head ).equals( disjointSet.find( tail ) ) )
+            {
+                disjointSet.union( head, tail );
+                spanningTree.addEdge( head, edge, tail );
+            }
+        }
+
+        return spanningTree;
     }
 
 }

Added: commons/sandbox/graph/trunk/src/test/java/org/apache/commons/graph/spanning/KruskalTestCase.java
URL: http://svn.apache.org/viewvc/commons/sandbox/graph/trunk/src/test/java/org/apache/commons/graph/spanning/KruskalTestCase.java?rev=1143237&view=auto
==============================================================================
--- commons/sandbox/graph/trunk/src/test/java/org/apache/commons/graph/spanning/KruskalTestCase.java
(added)
+++ commons/sandbox/graph/trunk/src/test/java/org/apache/commons/graph/spanning/KruskalTestCase.java
Wed Jul  6 01:18:25 2011
@@ -0,0 +1,104 @@
+package org.apache.commons.graph.spanning;
+
+/*
+ * 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.
+ */
+
+import static junit.framework.Assert.assertEquals;
+import static org.apache.commons.graph.spanning.Kruskal.minimumSpanningTree;
+
+import org.apache.commons.graph.SpanningTree;
+import org.apache.commons.graph.model.BaseLabeledVertex;
+import org.apache.commons.graph.model.BaseLabeledWeightedEdge;
+import org.apache.commons.graph.model.MutableSpanningTree;
+import org.apache.commons.graph.model.UndirectedMutableWeightedGraph;
+import org.junit.Test;
+
+public final class KruskalTestCase
+{
+
+    /**
+     * Test Graph and Prim's solution can be seen on
+     * <a href="http://en.wikipedia.org/wiki/Prim%27s_algorithm">Wikipedia</a>
+     */
+    @Test
+    public void verifyWikipediaMinimumSpanningTree()
+    {
+        UndirectedMutableWeightedGraph<BaseLabeledVertex, BaseLabeledWeightedEdge>
input
+            = new UndirectedMutableWeightedGraph<BaseLabeledVertex, BaseLabeledWeightedEdge>();
+
+        BaseLabeledVertex a = new BaseLabeledVertex( "A" );
+        BaseLabeledVertex b = new BaseLabeledVertex( "B" );
+        BaseLabeledVertex c = new BaseLabeledVertex( "C" );
+        BaseLabeledVertex d = new BaseLabeledVertex( "D" );
+        BaseLabeledVertex e = new BaseLabeledVertex( "E" );
+        BaseLabeledVertex f = new BaseLabeledVertex( "F" );
+        BaseLabeledVertex g = new BaseLabeledVertex( "G" );
+
+        input.addVertex( a );
+        input.addVertex( b );
+        input.addVertex( c );
+        input.addVertex( d );
+        input.addVertex( e );
+        input.addVertex( f );
+        input.addVertex( g );
+
+        input.addEdge( a, new BaseLabeledWeightedEdge( "a <-> b", 7D ), b );
+        input.addEdge( a, new BaseLabeledWeightedEdge( "a <-> d", 5D ), d );
+
+        input.addEdge( b, new BaseLabeledWeightedEdge( "b <-> c", 8D ), c );
+        input.addEdge( b, new BaseLabeledWeightedEdge( "b <-> d", 9D ), d );
+        input.addEdge( b, new BaseLabeledWeightedEdge( "b <-> e", 7D ), e );
+
+        input.addEdge( c, new BaseLabeledWeightedEdge( "c <-> e", 5D ), e );
+
+        input.addEdge( d, new BaseLabeledWeightedEdge( "d <-> e", 15D ), e );
+        input.addEdge( d, new BaseLabeledWeightedEdge( "d <-> f", 6D ), f );
+
+        input.addEdge( e, new BaseLabeledWeightedEdge( "e <-> f", 8D ), f );
+        input.addEdge( e, new BaseLabeledWeightedEdge( "e <-> g", 9D ), g );
+
+        input.addEdge( f, new BaseLabeledWeightedEdge( "f <-> g", 11D ), g );
+
+        // expected
+
+        MutableSpanningTree<BaseLabeledVertex, BaseLabeledWeightedEdge> expected =
+            new MutableSpanningTree<BaseLabeledVertex, BaseLabeledWeightedEdge>();
+
+        for ( BaseLabeledVertex vertex : input.getVertices() )
+        {
+            expected.addVertex( vertex );
+        }
+
+        expected.addEdge( a, new BaseLabeledWeightedEdge( "a <-> b", 7D ), b );
+        expected.addEdge( a, new BaseLabeledWeightedEdge( "a <-> d", 5D ), d );
+        expected.addEdge( b, new BaseLabeledWeightedEdge( "b <-> e", 9D ), e );
+        expected.addEdge( c, new BaseLabeledWeightedEdge( "c <-> e", 5D ), e );
+        expected.addEdge( d, new BaseLabeledWeightedEdge( "d <-> f", 6D ), f );
+        expected.addEdge( e, new BaseLabeledWeightedEdge( "e <-> g", 9D ), g );
+
+        // Actual
+
+        SpanningTree<BaseLabeledVertex, BaseLabeledWeightedEdge> actual = minimumSpanningTree(
input );
+
+        // assert!
+
+        assertEquals( expected, actual );
+    }
+
+}

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