public void testUndirectedGraphGnp1() {
GraphGenerator<Integer, DefaultEdge, Integer> gen =
new GnpRandomBipartiteGraphGenerator<>(4, 4, 0.5, SEED);
UndirectedGraph<Integer, DefaultEdge> g = new SimpleGraph<>(DefaultEdge.class);
gen.generateGraph(g, new IntegerVertexFactory(), null);
int[][] edges = {{1, 6}, {1, 7}, {1, 8}, {2, 5}, {2, 7}, {3, 5}, {3, 8}, {4, 6}, {4, 7}};
assertEquals(4 + 4, g.vertexSet().size());
for (int[] e : edges) {
assertTrue(g.containsEdge(e[0], e[1]));
}
assertEquals(edges.length, g.edgeSet().size());
}
/**
* Create a copy of a graph for internal use.
*
* @param graph the graph to copy.
* @return A copy of the graph projected to a SimpleGraph.
*/
private static <V, E> UndirectedGraph<V, E> copyAsSimpleGraph(UndirectedGraph<V, E> graph) {
UndirectedGraph<V, E> copy = new SimpleGraph<>(graph.getEdgeFactory());
if (graph instanceof SimpleGraph) {
Graphs.addGraph(copy, graph);
} else {
// project graph to SimpleGraph
Graphs.addAllVertices(copy, graph.vertexSet());
for (E e : graph.edgeSet()) {
V v1 = graph.getEdgeSource(e);
V v2 = graph.getEdgeTarget(e);
if ((v1 != v2) && !copy.containsEdge(e)) {
copy.addEdge(v1, v2);
}
}
}
return copy;
}
/**
* This method will return a list of vertices which represents the Eulerian circuit of the graph.
*
* @param g The graph to find an Eulerian circuit
* @return null if no Eulerian circuit exists, or a list of vertices representing the Eulerian
* circuit if one does exist
*/
public static <V, E> List<V> getEulerianCircuitVertices(UndirectedGraph<V, E> g) {
// If the graph is not Eulerian then just return a null since no
// Eulerian circuit exists
if (!isEulerian(g)) {
return null;
}
// The circuit will be represented by a linked list
List<V> path = new LinkedList<V>();
UndirectedGraph<V, E> sg = new UndirectedSubgraph<V, E>(g, null, null);
path.add(sg.vertexSet().iterator().next());
// Algorithm for finding an Eulerian circuit Basically this will find an
// arbitrary circuit, then it will find another arbitrary circuit until
// every edge has been traversed
while (sg.edgeSet().size() > 0) {
V v = null;
// Find a vertex which has an edge that hasn't been traversed yet,
// and keep its index position in the circuit list
int index = 0;
for (Iterator<V> iter = path.iterator(); iter.hasNext(); index++) {
v = iter.next();
if (sg.degreeOf(v) > 0) {
break;
}
}
// Finds an arbitrary circuit of the current vertex and
// appends this into the circuit list
while (sg.degreeOf(v) > 0) {
for (Iterator<V> iter = sg.vertexSet().iterator(); iter.hasNext(); ) {
V temp = iter.next();
if (sg.containsEdge(v, temp)) {
path.add(index, temp);
sg.removeEdge(v, temp);
v = temp;
break;
}
}
}
}
return path;
}