org.jgrapht.generate.ComplementGraphGenerator Maven / Gradle / Ivy
/*
* (C) Copyright 2017-2023, by Joris Kinable 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.generate;
import org.jgrapht.*;
import java.util.*;
/**
* Generator which produces the
* complement graph of a given input
* graph. The complement $\overline{G}$ of a graph $G$ consists of the same vertices as $G$, but
* whose edge set consists of the edges not in $G$.
*
* More formally, let $G = (V, E)$ be a graph and let $K$ consist of all 2-element subsets of $V$.
* Then $\overline{G} = (V, K \setminus E)$ is the complement of $G$, where $K \setminus E$ is the
* relative complement of $E$ in $K$. For directed graphs, the complement can be defined in the same
* way, as a directed graph on the same vertex set, using the set of all 2-element ordered pairs of
* $V$ in place of the set $K$ in the formula above.
*
* The complement is not defined for multigraphs. If a multigraph is provided as input to this
* generator, it will be treated as if it is a simple graph.
*
* @author Joris Kinable
*
*
* @param vertex type
* @param edge type
*/
public class ComplementGraphGenerator
implements GraphGenerator
{
private final Graph graph;
private final boolean generateSelfLoops;
/**
* Complement Graph Generator
*
* @param graph input graph
*/
public ComplementGraphGenerator(Graph graph)
{
this(graph, false);
}
/**
* Complement Graph Generator. If the target graph allows self-loops the complement of $G$ may
* be defined by adding a self-loop to every vertex that does not have one in $G$. This behavior
* can be controlled using the boolean generateSelfLoops.
*
* @param graph input graph
* @param generateSelfLoops indicator whether self loops should be generated. If false, no
* self-loops are generated, independent of whether the target graph supports self-loops.
*/
public ComplementGraphGenerator(Graph graph, boolean generateSelfLoops)
{
this.graph = GraphTests.requireDirectedOrUndirected(graph);
this.generateSelfLoops = generateSelfLoops;
}
@Override
public void generateGraph(Graph target, Map resultMap)
{
Graphs.addAllVertices(target, graph.vertexSet());
if (graph.getType().isDirected()) {
for (V u : graph.vertexSet())
for (V v : graph.vertexSet())
if (u == v)
continue;
else if (!graph.containsEdge(u, v))
target.addEdge(u, v);
} else { // undirected graph
List vertices = new ArrayList<>(graph.vertexSet());
for (int i = 0; i < vertices.size() - 1; i++) {
for (int j = i + 1; j < vertices.size(); j++) {
V u = vertices.get(i);
V v = vertices.get(j);
if (!graph.containsEdge(u, v))
target.addEdge(u, v);
}
}
}
if (generateSelfLoops && target.getType().isAllowingSelfLoops()) {
for (V v : graph.vertexSet()) {
if (!graph.containsEdge(v, v))
target.addEdge(v, v);
}
}
}
}