CycleWorkSpace.java

// *************************************************************************

public class CycleWorkSpace extends WorkSpace {

	public boolean AnyCycles;

	public int counter;

	public static final int WHITE = 0;

	public static final int GRAY = 1;

	public static final int BLACK = 2;

	public CycleWorkSpace() {
		AnyCycles = false;
		counter = 0;
	}

	public void init_vertex(Vertex v) {
		v.VertexCycle = Integer.MAX_VALUE;
		v.VertexColor = WHITE; // initialize to white color
	}

	public void preVisitAction(Vertex v) {

		// This assigns the values on the way in
		if (v.visited != true) { // if it has not been visited then set the
			// VertexCycle accordingly
			v.VertexCycle = counter++;
			v.VertexColor = GRAY; // we make the vertex gray
		}
	}

	public void postVisitAction(Vertex v) {
		v.VertexColor = BLACK; // we are done visiting so make it black
		counter--;
	} // of postVisitAction

	public void checkNeighborAction(Vertex vsource, Vertex vtarget) {
		// if the graph is directed is enough to check that the source node
		// is gray and the adyacent is gray also to find a cycle
		// if the graph is undirected we need to check that the adyacent is not
		// the father, if it is the father the difference in the VertexCount is
		// only one.

		// directed
		if ((vsource.VertexColor == GRAY) && (vtarget.VertexColor == GRAY)) {
			AnyCycles = true;
		}
		// undirected case
		if ((vsource.VertexColor == GRAY) && (vtarget.VertexColor == GRAY)
				&& vsource.VertexCycle != vtarget.VertexCycle + 1) {
			AnyCycles = true;
		}

	} // of checkNeighboor

}