package org.neo4j.graphalgo.impl.util;
import java.util.LinkedList;
import java.util.Queue;
import org.neo4j.graphdb.traversal.TraversalBranch;
import org.neo4j.graphdb.traversal.BranchSelector;
/**
* A preorder depth first selector which detects "super nodes", i.e. nodes
* which has many relationships. It delays traversing those super nodes until
* after all non-super nodes have been traversed.
*
* @author Mattias Persson
* @author Tobias Ivarsson
*/
public class LiteDepthFirstSelector implements BranchSelector
{
private final Queue<TraversalBranch> superNodes = new LinkedList<TraversalBranch>();
private TraversalBranch current;
private final int threshold;
public LiteDepthFirstSelector( TraversalBranch startSource, int startThreshold )
{
this.current = startSource;
this.threshold = startThreshold;
}
public TraversalBranch next()
{
TraversalBranch result = null;
while ( result == null )
{
if ( current == null )
{
current = superNodes.poll();
if ( current == null )
{
return null;
}
}
else if ( current.expanded() > 0 && current.expanded() % threshold == 0 )
{
superNodes.add( current );
current = current.parent();
continue;
}
TraversalBranch next = current.next();
if ( next == null )
{
current = current.parent();
continue;
}
else
{
current = next;
}
if ( current != null )
{
result = current;
}
}
return result;
}
}