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<?php
/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */
// +-----------------------------------------------------------------------------+
// | Copyright (c) 2003 Sérgio Gonçalves Carvalho |
// +-----------------------------------------------------------------------------+
// | This file is part of Structures_Graph. |
// | |
// | Structures_Graph 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. |
// | |
// | Structures_Graph 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 Structures_Graph; if not, write to the Free Software |
// | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
// | 02111-1307 USA |
// +-----------------------------------------------------------------------------+
// | Author: Sérgio Carvalho <sergio.carvalho@portugalmail.com> |
// +-----------------------------------------------------------------------------+
//
/**
* This file contains the definition of the Structures_Graph_Manipulator_TopologicalSorter class.
*
* @package Structures_Graph
*/
require_once 'PEAR.php';
require_once 'Structures/Graph.php';
require_once 'Structures/Graph/Node.php';
require_once 'Structures/Graph/Manipulator/AcyclicTest.php';
/**
* The Structures_Graph_Manipulator_TopologicalSorter is a manipulator
* which is able to return the set of nodes in a graph, sorted by topological
* order.
*
* A graph may only be sorted topologically iff it's a DAG. You can test it
* with the Structures_Graph_Manipulator_AcyclicTest.
*
* @author Sérgio Carvalho <sergio.carvalho@portugalmail.com>
* @copyright (c) 2004 by Sérgio Carvalho
* @see Structures_Graph_Manipulator_AcyclicTest
* @package Structures_Graph
*/
class Structures_Graph_Manipulator_TopologicalSorter
{
/**
* This is a variant of Structures_Graph::inDegree which does
* not count nodes marked as visited.
*
* @param object $node Node to check
*
* @return integer Number of non-visited nodes that link to this one
*/
protected static function _nonVisitedInDegree(&$node)
{
$result = 0;
$graphNodes =& $node->_graph->getNodes();
foreach (array_keys($graphNodes) as $key) {
if ((!$graphNodes[$key]->getMetadata('topological-sort-visited'))
&& $graphNodes[$key]->connectsTo($node)
) {
$result++;
}
}
return $result;
}
/**
* Sort implementation
*
* @param object $graph Graph to sort
*
* @return void
*/
protected static function _sort(&$graph)
{
// Mark every node as not visited
$nodes =& $graph->getNodes();
$nodeKeys = array_keys($nodes);
$refGenerator = array();
foreach ($nodeKeys as $key) {
$refGenerator[] = false;
$nodes[$key]->setMetadata(
'topological-sort-visited',
$refGenerator[sizeof($refGenerator) - 1]
);
}
// Iteratively peel off leaf nodes
$topologicalLevel = 0;
do {
// Find out which nodes are leafs (excluding visited nodes)
$leafNodes = array();
foreach ($nodeKeys as $key) {
if ((!$nodes[$key]->getMetadata('topological-sort-visited'))
&& static::_nonVisitedInDegree($nodes[$key]) == 0
) {
$leafNodes[] =& $nodes[$key];
}
}
// Mark leafs as visited
$refGenerator[] = $topologicalLevel;
for ($i = sizeof($leafNodes) - 1; $i>=0; $i--) {
$visited =& $leafNodes[$i]->getMetadata('topological-sort-visited');
$visited = true;
$leafNodes[$i]->setMetadata('topological-sort-visited', $visited);
$leafNodes[$i]->setMetadata(
'topological-sort-level',
$refGenerator[sizeof($refGenerator) - 1]
);
}
$topologicalLevel++;
} while (sizeof($leafNodes) > 0);
// Cleanup visited marks
foreach ($nodeKeys as $key) {
$nodes[$key]->unsetMetadata('topological-sort-visited');
}
}
/**
* Sort returns the graph's nodes, sorted by topological order.
*
* The result is an array with as many entries as topological levels.
* Each entry in this array is an array of nodes within
* the given topological level.
*
* @param object $graph Graph to sort
*
* @return array The graph's nodes, sorted by topological order.
*/
public static function sort(&$graph)
{
// We only sort graphs
if (!is_a($graph, 'Structures_Graph')) {
return Pear::raiseError(
'Structures_Graph_Manipulator_TopologicalSorter::sort received'
. ' an object that is not a Structures_Graph',
STRUCTURES_GRAPH_ERROR_GENERIC
);
}
if (!Structures_Graph_Manipulator_AcyclicTest::isAcyclic($graph)) {
return Pear::raiseError(
'Structures_Graph_Manipulator_TopologicalSorter::sort'
. ' received an graph that has cycles',
STRUCTURES_GRAPH_ERROR_GENERIC
);
}
Structures_Graph_Manipulator_TopologicalSorter::_sort($graph);
$result = array();
// Fill out result array
$nodes =& $graph->getNodes();
$nodeKeys = array_keys($nodes);
foreach ($nodeKeys as $key) {
if (!array_key_exists($nodes[$key]->getMetadata('topological-sort-level'), $result)) {
$result[$nodes[$key]->getMetadata('topological-sort-level')]
= array();
}
$result[$nodes[$key]->getMetadata('topological-sort-level')][]
=& $nodes[$key];
$nodes[$key]->unsetMetadata('topological-sort-level');
}
return $result;
}
}
?>
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