net.automatalib.util.graphs.traversal.DepthFirstIterator Maven / Gradle / Ivy
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This artifact provides various common utility operations for analyzing and manipulating
automata and graphs, such as traversal, minimization and copying.
/* Copyright (C) 2013 TU Dortmund
* This file is part of AutomataLib, http://www.automatalib.net/.
*
* AutomataLib is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 3.0 as published by the Free Software Foundation.
*
* AutomataLib 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 AutomataLib; if not, see
* http://www.gnu.de/documents/lgpl.en.html.
*/
package net.automatalib.util.graphs.traversal;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import java.util.NoSuchElementException;
import net.automatalib.commons.util.mappings.MutableMapping;
import net.automatalib.graphs.IndefiniteGraph;
import net.automatalib.util.traversal.VisitedState;
final class DepthFirstIterator implements Iterator {
private final MutableMapping visited;
private final Deque> dfsStack
= new ArrayDeque<>();
private final IndefiniteGraph graph;
public DepthFirstIterator(IndefiniteGraph graph, Collection start) {
this.graph = graph;
this.visited = graph.createStaticNodeMapping();
for(N startNode : start)
dfsStack.push(new SimpleDFRecord(startNode));
}
@Override
public boolean hasNext() {
return !dfsStack.isEmpty();
}
@Override
public N next() {
SimpleDFRecord rec = dfsStack.peek();
if(rec == null)
throw new NoSuchElementException();
N result;
if(rec.start(graph)) {
result = rec.node;
visited.put(result, VisitedState.VISITED);
}
else {
E edge = rec.nextEdge();
result = graph.getTarget(edge);
if(visited.get(result) != VisitedState.VISITED)
dfsStack.push(new SimpleDFRecord(result));
}
cleanup();
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
/*
* Performs a cleanup operation on the stack. After a cleanup, the stack will be either empty,
* or the top record on the step will be:
* - an unstarted record of a node that has NOT been visited, or,
* - a started record of a node with at least one outgoing edge to a node that has not been visited
*/
private void cleanup() {
SimpleDFRecord rec;
while((rec = dfsStack.peek()) != null) {
if(!rec.wasStarted()) {
if(visited.get(rec.node) != VisitedState.VISITED)
return;
}
else {
while(rec.hasNextEdge()) {
E edge = rec.nextEdge();
N tgt = graph.getTarget(edge);
if(visited.get(tgt) != VisitedState.VISITED) {
rec.retract(edge);
return;
}
}
}
dfsStack.pop();
}
}
}