/*
* Copyright (c) 2016 Vivid Solutions.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
*
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.locationtech.jts.planargraph.algorithm;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Stack;
import org.locationtech.jts.planargraph.DirectedEdge;
import org.locationtech.jts.planargraph.DirectedEdgeStar;
import org.locationtech.jts.planargraph.Edge;
import org.locationtech.jts.planargraph.GraphComponent;
import org.locationtech.jts.planargraph.Node;
import org.locationtech.jts.planargraph.PlanarGraph;
import org.locationtech.jts.planargraph.Subgraph;
/**
* 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);
}
}
}