org.jbpt.algo.tree.tctree.AbstractDFS Maven / Gradle / Ivy

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package org.jbpt.algo.tree.tctree;

import org.jbpt.graph.abs.IEdge;
import org.jbpt.graph.abs.IGraph;
import org.jbpt.hypergraph.abs.IVertex;

/**
 * A standard Depth-first-search (DFS) implementation. 
 * It implements the same dummy-methods as the DFS algorithm in {@link y.algo.Dfs}, 
 * but operates on a given adjacency structure to determine the order in which paths are generated.
 * 
 * @author Martin Mader
 * @author Christian Wiggert
 */
public class AbstractDFS, V extends IVertex> {
	protected final V INVALID_NODE = null;
	protected final E INVALID_EDGE = null;
	
	//Vertex not yet visited
	public static final int WHITE = 0;
	// Vertex visited, but not yet finished
	public static final int GRAY = 1;
	// Vertex processed completely
	public static final int BLACK = 2;
	protected static final int EDGE_NOT_VISITED = 0;
	// Tree edge
	public static final int TREE_EDGE = 1;
	// Back edge
	public static final int BACK_EDGE = 2;
	// Adjacency Map
	protected NodeMap adj;
	// The graph to operate on
	protected IGraph g;
	// The MetaInfoContainer for the additional maps related to the graph
	protected MetaInfoContainer meta;
	// NodeMap storing DFS-Numbers
	protected NodeMap dfsNumMap;
	// NodeMap storing Completion Numbers
	protected NodeMap complNumMap;
	// NodeMap storing current vertex status: WHITE, GRAY, or BLACK
	protected NodeMap nodeStateMap;
	// EdgeMap storing current edge type: EDGE_NOT_VISITED, TREE_EDGE or BACK_EDGE
	protected EdgeMap edgeTypeMap;
	private int dfsNum = 0;
	private int complNum = 0;
	
	/**
	 * Creates an instance of DFS which operates on the given graph and adjacency structure.
	 * 
	 * @param graph The graph on which to perform DFS.
	 * @param adjMap The adjacency structure to be used.
	 * 					in each entry must be contained an 
	 * 					{@link y.base.EdgeList} 
	 * 					of adjacent neighbors. DFS traverses edges 
	 * 					the according order.				
	 */
	public AbstractDFS(IGraph graph, MetaInfoContainer container, NodeMap adjMap) {
		g = graph;
		adj = adjMap;
		meta = container;
		nodeStateMap = this.createNodeMap(g);
		dfsNumMap = this.createNodeMap(g);
		complNumMap = this.createNodeMap(g);
		for (V node:g.getVertices()){
			nodeStateMap.put(node, WHITE);
			dfsNumMap.put(node, -1);
			complNumMap.put(node, -1);
		}
		edgeTypeMap = this.createEdgeMap(g);
		for (E edge:g.getEdges()){
			edgeTypeMap.put(edge, EDGE_NOT_VISITED);
		}
		// add data provider
		meta.setMetaInfo(MetaInfo.DFS_NUM, dfsNumMap);
		meta.setMetaInfo(MetaInfo.DFS_COMPL_NUM, complNumMap);
		meta.setMetaInfo(MetaInfo.DFS_NODE_STATE, nodeStateMap);
		meta.setMetaInfo(MetaInfo.DFS_EDGE_TYPE, edgeTypeMap);
	}
	
	/**
	 * starts a depth-first-search (DFS) beginning at the given 
	 *  
	 * @param root the root node of the DFS
	 */
	public void start(V root) {
		dfsNum = 0;
		complNum = 0;
		dfs(root);
	}
	
	@SuppressWarnings("unchecked")
	protected void dfs(V v){
		dfsNum++;
		dfsNumMap.put(v, dfsNum);
		nodeStateMap.put(v, GRAY);
		EdgeList adjV = (EdgeList) adj.get(v);
		
		//System.out.println(v + ": " + adjV);
		preVisit(v, (Integer) dfsNumMap.get(v));
		
		for (E e:adjV){
			// traverse only not yet visited edges
			//System.out.println("Visit: " + e);
			if ((Integer) edgeTypeMap.get(e) == EDGE_NOT_VISITED) {
				
				V w = e.getOtherVertex(v);
				// re-orient edge
				e.setVertices(v,w);
				
				if ((Integer) nodeStateMap.get(w) == WHITE) {
					// tree edge found -> traverse edge
					edgeTypeMap.put(e, TREE_EDGE);

					preTraverse(e, w, true);

					dfs(w);

					postTraverse(e, w);

				} else {
					// back edge found
					edgeTypeMap.put(e, BACK_EDGE);

					preTraverse(e, w, false);
				}
			}
			
		}
		
		// backtrack
		nodeStateMap.put(v, BLACK);
		complNum++;
		complNumMap.put(v, complNum);
		
		postVisit(v, (Integer) dfsNumMap.get(v), (Integer) complNumMap.get(v));
		
		
	}
	
	protected void preVisit(V v, int dfsNumber) {}
	
	protected  void preTraverse(E e, V w, boolean treeEdge) {}
	
	protected  void postTraverse(E e, V w) {}
	
	protected  void postVisit(V v, int dfsNumber, int complNumber) {}

	public EdgeMap getEdgeTypeMap() {
		return edgeTypeMap;
	}
	
	protected EdgeMap createEdgeMap(IGraph g) {
		EdgeMap map = new EdgeMap();
		for (E e:g.getEdges()) {
			map.put(e, null);
		}
		return map;
	}
	
	protected NodeMap createNodeMap(IGraph g) {
		NodeMap map = new NodeMap();
		for (V v:g.getVertices()) {
			map.put(v, null);
		}
		return map;
	}

}