flow/src/main/java/org/apache/commons/graph/flow/DefaultMaxFlowAlgorithmSelector.java

package org.apache.commons.graph.flow;

/*
 * 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 org.apache.commons.graph.Graphs.populate;
import static org.apache.commons.graph.utils.Assertions.checkNotNull;
import static org.apache.commons.graph.visit.GraphVisitor.visit;

import org.apache.commons.graph.DirectedGraph;
import org.apache.commons.graph.Mapper;
import org.apache.commons.graph.VertexPair;
import org.apache.commons.graph.builder.AbstractGraphConnection;
import org.apache.commons.graph.math.monoid.OrderedMonoid;
import org.apache.commons.graph.model.DirectedMutableGraph;

/**
 * {@link MaxFlowAlgorithmSelector} implementation.
 *
 * @param <V> the Graph vertices type
 * @param <WE> the Graph edges type
 * @param <W> the Graph weight type
 */
final class DefaultMaxFlowAlgorithmSelector<V, WE, W>
    implements MaxFlowAlgorithmSelector<V, WE, W>
{

    private final DirectedGraph<V, WE> graph;

    private final Mapper<WE, W> weightedEdges;

    private final V source;

    private final V target;

    public DefaultMaxFlowAlgorithmSelector( DirectedGraph<V, WE> graph, Mapper<WE, W> weightedEdges, V source, V target )
    {
        this.graph = graph;
        this.weightedEdges = weightedEdges;
        this.source = source;
        this.target = target;
    }

    /**
     * {@inheritDoc}
     */
    public <WO extends OrderedMonoid<W>> W applyingFordFulkerson( WO weightOperations )
    {
        final WO checkedWeightOperations = checkNotNull( weightOperations, "Weight operations can not be null to find the max flow in the graph" );

        // create flow network
        final DirectedGraph<V, EdgeWrapper<WE>> flowNetwork = newFlowNetwok( graph, checkedWeightOperations );

        // create flow network handler
        final FlowNetworkHandler<V, EdgeWrapper<WE>, W> flowNetworkHandler =
                        new FlowNetworkHandler<V, EdgeWrapper<WE>, W>( flowNetwork, source, target, checkedWeightOperations, new MapperWrapper<WE, W, WO>( checkedWeightOperations, weightedEdges ) );

        // perform depth first search
        visit( flowNetwork ).from( source ).applyingDepthFirstSearch( flowNetworkHandler );

        while ( flowNetworkHandler.hasAugmentingPath() )
        {
            // update flow network
            flowNetworkHandler.updateResidualNetworkWithCurrentAugmentingPath();
            // look for another augmenting path with depth first search
            visit( flowNetwork ).from( source ).applyingDepthFirstSearch( flowNetworkHandler );
        }

        return flowNetworkHandler.onCompleted();
    }

    /**
     * {@inheritDoc}
     */
    public <WO extends OrderedMonoid<W>> W applyingEdmondsKarp( WO weightOperations )
    {
        final WO checkedWeightOperations = checkNotNull( weightOperations, "Weight operations can not be null to find the max flow in the graph" );

        // create flow network
        final DirectedGraph<V, EdgeWrapper<WE>> flowNetwork = newFlowNetwok( graph, checkedWeightOperations );

        // create flow network handler
        final FlowNetworkHandler<V, EdgeWrapper<WE>, W> flowNetworkHandler =
                        new FlowNetworkHandler<V, EdgeWrapper<WE>, W>( flowNetwork, source, target, checkedWeightOperations, new MapperWrapper<WE, W, WO>( checkedWeightOperations, weightedEdges ) );

        // perform breadth first search
        visit( flowNetwork ).from( source ).applyingBreadthFirstSearch( flowNetworkHandler );

        while ( flowNetworkHandler.hasAugmentingPath() )
        {
            // update flow network
            flowNetworkHandler.updateResidualNetworkWithCurrentAugmentingPath();
            // look for another augmenting path with breadth first search
            visit( flowNetwork ).from( source ).applyingBreadthFirstSearch( flowNetworkHandler );
        }

        return flowNetworkHandler.onCompleted();
    }

    private <WO extends OrderedMonoid<W>> DirectedGraph<V, EdgeWrapper<WE>> newFlowNetwok( final DirectedGraph<V, WE> graph,
                                                                                           final WO weightOperations )
    {
        return populate( new DirectedMutableGraph<V, EdgeWrapper<WE>>() )
               .withConnections( new AbstractGraphConnection<V, EdgeWrapper<WE>>()
        {
            @Override
            public void connect()
            {
                // vertices
                for ( V vertex : graph.getVertices() )
                {
                    addVertex( vertex );
                }

                // edges
                for ( WE edge : graph.getEdges() )
                {
                    VertexPair<V> edgeVertices = graph.getVertices( edge );
                    V head = edgeVertices.getHead();
                    V tail = edgeVertices.getTail();

                    addEdge( new EdgeWrapper<WE>( edge ) ).from( head ).to( tail );

                    if ( graph.getEdge( tail, head ) == null )
                    {
                        // complete the flow network with a zero-capacity inverse edge
                        addEdge( new EdgeWrapper<WE>() ).from( tail ).to( head );
                    }
                }
            }
        } );
    }

    private static final class EdgeWrapper<WE>
    {

        private final WE wrapped;

        public EdgeWrapper()
        {
            this( null );
        }

        public EdgeWrapper( WE wrapped )
        {
            this.wrapped = wrapped;
        }

        public WE getWrapped()
        {
            return wrapped;
        }

    }

    @SuppressWarnings( "serial" ) //the algorithm isn't serializable.
    private static final class MapperWrapper<WE, W, WO extends OrderedMonoid<W>>
        implements Mapper<EdgeWrapper<WE>, W>
    {

        private final WO weightOperations;

        private final Mapper<WE, W> weightedEdges;

        public MapperWrapper( WO weightOperations, Mapper<WE, W> weightedEdges )
        {
            this.weightOperations = weightOperations;
            this.weightedEdges = weightedEdges;
        }

        public W map( EdgeWrapper<WE> input )
        {
            if ( input.getWrapped() == null )
            {
                return weightOperations.identity();
            }
            return weightedEdges.map( input.getWrapped() );
        }

    }

}