135 lines
5.6 KiB
PHP
135 lines
5.6 KiB
PHP
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<?php
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/* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */
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// +-----------------------------------------------------------------------------+
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// | Copyright (c) 2003 S<>rgio Gon<6F>alves Carvalho |
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// +-----------------------------------------------------------------------------+
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// | This file is part of Structures_Graph. |
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// | |
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// | Structures_Graph is free software; you can redistribute it and/or modify |
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// | it under the terms of the GNU Lesser General Public License as published by |
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// | the Free Software Foundation; either version 2.1 of the License, or |
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// | (at your option) any later version. |
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// | |
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// | Structures_Graph is distributed in the hope that it will be useful, |
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// | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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// | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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// | GNU Lesser General Public License for more details. |
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// | |
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// | You should have received a copy of the GNU Lesser General Public License |
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// | along with Structures_Graph; if not, write to the Free Software |
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// | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
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// | 02111-1307 USA |
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// +-----------------------------------------------------------------------------+
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// | Author: S<>rgio Carvalho <sergio.carvalho@portugalmail.com> |
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// +-----------------------------------------------------------------------------+
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//
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/**
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* This file contains the definition of the Structures_Graph_Manipulator_AcyclicTest graph manipulator.
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*
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* @see Structures_Graph_Manipulator_AcyclicTest
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* @package Structures_Graph
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*/
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/* dependencies {{{ */
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/** */
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require_once 'PEAR.php';
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/** */
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require_once 'Structures/Graph.php';
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/** */
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require_once 'Structures/Graph/Node.php';
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/* }}} */
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/* class Structures_Graph_Manipulator_AcyclicTest {{{ */
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/**
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* The Structures_Graph_Manipulator_AcyclicTest is a graph manipulator
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* which tests whether a graph contains a cycle.
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*
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* The definition of an acyclic graph used in this manipulator is that of a
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* DAG. The graph must be directed, or else it is considered cyclic, even when
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* there are no arcs.
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*
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* @author S<EFBFBD>rgio Carvalho <sergio.carvalho@portugalmail.com>
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* @copyright (c) 2004 by S<EFBFBD>rgio Carvalho
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* @package Structures_Graph
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*/
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class Structures_Graph_Manipulator_AcyclicTest {
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/* _nonVisitedInDegree {{{ */
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/**
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*
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* This is a variant of Structures_Graph::inDegree which does
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* not count nodes marked as visited.
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*
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* @return integer Number of non-visited nodes that link to this one
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*/
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protected static function _nonVisitedInDegree(&$node) {
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$result = 0;
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$graphNodes =& $node->_graph->getNodes();
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foreach (array_keys($graphNodes) as $key) {
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if ((!$graphNodes[$key]->getMetadata('acyclic-test-visited')) && $graphNodes[$key]->connectsTo($node)) $result++;
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}
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return $result;
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}
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/* }}} */
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/* _isAcyclic {{{ */
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/**
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* Check if the graph is acyclic
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*/
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protected static function _isAcyclic(&$graph) {
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// Mark every node as not visited
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$nodes =& $graph->getNodes();
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$nodeKeys = array_keys($nodes);
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$refGenerator = array();
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foreach($nodeKeys as $key) {
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$refGenerator[] = false;
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$nodes[$key]->setMetadata('acyclic-test-visited', $refGenerator[sizeof($refGenerator) - 1]);
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}
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// Iteratively peel off leaf nodes
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do {
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// Find out which nodes are leafs (excluding visited nodes)
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$leafNodes = array();
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foreach($nodeKeys as $key) {
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if ((!$nodes[$key]->getMetadata('acyclic-test-visited')) && Structures_Graph_Manipulator_AcyclicTest::_nonVisitedInDegree($nodes[$key]) == 0) {
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$leafNodes[] =& $nodes[$key];
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}
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}
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// Mark leafs as visited
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for ($i=sizeof($leafNodes) - 1; $i>=0; $i--) {
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$visited =& $leafNodes[$i]->getMetadata('acyclic-test-visited');
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$visited = true;
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$leafNodes[$i]->setMetadata('acyclic-test-visited', $visited);
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}
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} while (sizeof($leafNodes) > 0);
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// If graph is a DAG, there should be no non-visited nodes. Let's try to prove otherwise
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$result = true;
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foreach($nodeKeys as $key) if (!$nodes[$key]->getMetadata('acyclic-test-visited')) $result = false;
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// Cleanup visited marks
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foreach($nodeKeys as $key) $nodes[$key]->unsetMetadata('acyclic-test-visited');
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return $result;
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}
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/* }}} */
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/* isAcyclic {{{ */
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/**
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*
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* isAcyclic returns true if a graph contains no cycles, false otherwise.
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*
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* @return boolean true iff graph is acyclic
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*/
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public static function isAcyclic(&$graph) {
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// We only test graphs
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if (!is_a($graph, 'Structures_Graph')) return Pear::raiseError('Structures_Graph_Manipulator_AcyclicTest::isAcyclic received an object that is not a Structures_Graph', STRUCTURES_GRAPH_ERROR_GENERIC);
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if (!$graph->isDirected()) return false; // Only directed graphs may be acyclic
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return Structures_Graph_Manipulator_AcyclicTest::_isAcyclic($graph);
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}
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/* }}} */
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}
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/* }}} */
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?>
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