org.jgrapht.alg.cycle.StackBFSFundamentalCycleBasis Maven / Gradle / Ivy
/*
* (C) Copyright 2016-2018, by Dimitrios Michail and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
package org.jgrapht.alg.cycle;
import org.jgrapht.*;
import java.util.*;
/**
* Generate a set of fundamental cycles by building a spanning tree (forest) using an implementation
* of BFS using a LIFO Stack. The implementation first constructs the spanning forest and then
* builds the fundamental-cycles set. It supports graphs with self-loops and/or graphs with multiple
* (parallel) edges.
*
*
* The algorithm constructs the same fundamental cycle basis as the algorithm in the following
* paper: K. Paton, An algorithm for finding a fundamental set of cycles for an undirected linear
* graph, Comm. ACM 12 (1969), pp. 514-518.
*
*
* The total length of the fundamental-cycle set can be as large as $O(n^3)$ where $n$ is the number
* of vertices of the graph.
*
* @param the vertex type
* @param the edge type
*
* @author Dimitrios Michail
* @since October 2016
*/
public class StackBFSFundamentalCycleBasis
extends
AbstractFundamentalCycleBasis
{
/**
* Constructor
*
* @param graph the input graph
*/
public StackBFSFundamentalCycleBasis(Graph graph)
{
super(graph);
}
/**
* Compute a spanning forest of the graph using a stack (LIFO) based BFS implementation.
*
*
* The representation assumes that the map contains the predecessor edge of each vertex in the
* forest. The predecessor edge is the forest edge that was used to discover the vertex. If no
* such edge was used (the vertex is a leaf in the forest) then the corresponding entry must be
* null.
*
* @return a map representation of a spanning forest.
*/
@Override
protected Map computeSpanningForest()
{
Map pred = new HashMap<>();
ArrayDeque stack = new ArrayDeque<>();
for (V s : graph.vertexSet()) {
// loop over connected-components
if (pred.containsKey(s)) {
continue;
}
// add s in stack
pred.put(s, null);
stack.push(s);
// start traversal
while (!stack.isEmpty()) {
V v = stack.pop();
for (E e : graph.edgesOf(v)) {
V u = Graphs.getOppositeVertex(graph, e, v);
if (!pred.containsKey(u)) {
pred.put(u, e);
stack.push(u);
}
}
}
}
return pred;
}
}