/* * The JTS Topology Suite is a collection of Java classes that * implement the fundamental operations required to validate a given * geo-spatial data set to a known topological specification. * * Copyright (C) 2001 Vivid Solutions * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * For more information, contact: * * Vivid Solutions * Suite #1A * 2328 Government Street * Victoria BC V8T 5G5 * Canada * * (250)385-6040 * www.vividsolutions.com */ package com.vividsolutions.jts.planargraph.algorithm; import java.util.*; import com.vividsolutions.jts.planargraph.*; /** * Finds all connected {@link Subgraph}s of a {@link PlanarGraph}. * <p> * <b>Note:</b> uses the <code>isVisited</code> flag on the nodes. */ public class ConnectedSubgraphFinder { private PlanarGraph graph; public ConnectedSubgraphFinder(PlanarGraph graph) { this.graph = graph; } public List getConnectedSubgraphs() { List subgraphs = new ArrayList(); GraphComponent.setVisited(graph.nodeIterator(), false); for (Iterator i = graph.edgeIterator(); i.hasNext(); ) { Edge e = (Edge) i.next(); Node node = e.getDirEdge(0).getFromNode(); if (! node.isVisited()) { subgraphs.add(findSubgraph(node)); } } return subgraphs; } private Subgraph findSubgraph(Node node) { Subgraph subgraph = new Subgraph(graph); addReachable(node, subgraph); return subgraph; } /** * Adds all nodes and edges reachable from this node to the subgraph. * Uses an explicit stack to avoid a large depth of recursion. * * @param node a node known to be in the subgraph */ private void addReachable(Node startNode, Subgraph subgraph) { Stack nodeStack = new Stack(); nodeStack.add(startNode); while (! nodeStack.empty()) { Node node = (Node) nodeStack.pop(); addEdges(node, nodeStack, subgraph); } } /** * Adds the argument node and all its out edges to the subgraph. * @param node the node to add * @param nodeStack the current set of nodes being traversed */ private void addEdges(Node node, Stack nodeStack, Subgraph subgraph) { node.setVisited(true); for (Iterator i = ((DirectedEdgeStar) node.getOutEdges()).iterator(); i.hasNext(); ) { DirectedEdge de = (DirectedEdge) i.next(); subgraph.add(de.getEdge()); Node toNode = de.getToNode(); if (! toNode.isVisited()) nodeStack.push(toNode); } } }