org.jgrapht.alg.interfaces.PartitioningAlgorithm Maven / Gradle / Ivy
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/*
* (C) Copyright 2018-2023, by Alexandru Valeanu and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* See the CONTRIBUTORS.md file distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0, or the
* GNU Lesser General Public License v2.1 or later
* which is available at
* http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
*
* SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
*/
package org.jgrapht.alg.interfaces;
import java.io.*;
import java.util.*;
import java.util.stream.*;
/**
* Algorithm to compute a vertex partitioning of a graph.
*
* @param vertex the graph vertex type
*
* @author Alexandru Valeanu
*/
public interface PartitioningAlgorithm
{
/**
* Computes a vertex partitioning.
*
* @return a vertex partitioning
*/
Partitioning getPartitioning();
/**
* Check if the given vertex partitioning is valid.
*
* @param partitioning the input vertex partitioning
* @return true if the input partitioning is valid, false otherwise
*/
boolean isValidPartitioning(Partitioning partitioning);
/**
* A graph partitioning.
*
* @param the vertex type
*/
interface Partitioning
extends Iterable>
{
/**
* Get the number of partitions.
*
* @return the number of partitions
*/
int getNumberPartitions();
/**
* Get the index-th partition (0-based).
*
* @param index index of the partition to return
* @return the index-th partition
* @throws IndexOutOfBoundsException if the index is out of range
* (index < 0 || index >= getNumberPartitions()
)
*/
Set getPartition(int index);
/**
* Get the partitions. This method returns a partitioning of the vertices in the graph into
* disjoint partitions.
*
* @return a list of partitions
*/
default List> getPartitions()
{
final int n = getNumberPartitions();
List> partitions = new ArrayList<>(n);
for (int i = 0; i < n; i++) {
partitions.add(getPartition(i));
}
return partitions;
}
}
/**
* Default implementation of a vertex partition
*
* @param the vertex type
*/
class PartitioningImpl
implements Partitioning, Serializable
{
private static final long serialVersionUID = 3702471090706836080L;
/* Partitioning classes */
private final List> classes;
/**
* Construct a new vertex partitioning.
*
* @param classes the partition classes
* @throws NullPointerException if {@code classes} is {@code null}
*/
public PartitioningImpl(List> classes)
{
this.classes = Collections.unmodifiableList(
Objects.requireNonNull(classes).stream().map(Collections::unmodifiableSet).collect(
Collectors.toList()));
}
/**
* Construct a new vertex partitioning.
*
* @param vertexToPartitionMap the vertex to partition index map
* @throws NullPointerException if {@code vertexToPartitionMap} is {@code null}
*/
public PartitioningImpl(Map vertexToPartitionMap)
{
Objects.requireNonNull(vertexToPartitionMap);
Map> partitionIndexToVertexMap = new HashMap<>();
for (Map.Entry entry : vertexToPartitionMap.entrySet()) {
partitionIndexToVertexMap
.computeIfAbsent(entry.getValue(), x -> new HashSet<>()).add(entry.getKey());
}
this.classes = Collections.unmodifiableList(
partitionIndexToVertexMap
.values().stream().map(Collections::unmodifiableSet)
.collect(Collectors.toList()));
}
/**
* {@inheritDoc}
*/
@Override
public int getNumberPartitions()
{
return classes.size();
}
/**
* {@inheritDoc}
*/
@Override
public Set getPartition(int index)
{
if (index < 0 || index >= classes.size()) {
throw new IndexOutOfBoundsException(index + " is not valid");
}
return classes.get(index);
}
/**
* {@inheritDoc}
*/
@Override
public String toString()
{
return "Partition [number-of-partitions=" + getNumberPartitions() + ", partitions="
+ classes + "]";
}
/**
* {@inheritDoc}
*/
@Override
public Iterator> iterator()
{
return classes.iterator();
}
}
}