1 | <?php |
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2 | /* vim: set expandtab tabstop=4 shiftwidth=4 foldmethod=marker: */ |
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3 | // +-----------------------------------------------------------------------------+ |
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4 | // | Copyright (c) 2003 Sérgio Gonçalves Carvalho | |
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5 | // +-----------------------------------------------------------------------------+ |
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6 | // | This file is part of Structures_Graph. | |
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7 | // | | |
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8 | // | Structures_Graph is free software; you can redistribute it and/or modify | |
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9 | // | it under the terms of the GNU Lesser General Public License as published by | |
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10 | // | the Free Software Foundation; either version 2.1 of the License, or | |
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11 | // | (at your option) any later version. | |
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12 | // | | |
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13 | // | Structures_Graph is distributed in the hope that it will be useful, | |
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14 | // | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
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15 | // | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
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16 | // | GNU Lesser General Public License for more details. | |
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17 | // | | |
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18 | // | You should have received a copy of the GNU Lesser General Public License | |
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19 | // | along with Structures_Graph; if not, write to the Free Software | |
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20 | // | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
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21 | // | 02111-1307 USA | |
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22 | // +-----------------------------------------------------------------------------+ |
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23 | // | Author: Sérgio Carvalho <sergio.carvalho@portugalmail.com> | |
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24 | // +-----------------------------------------------------------------------------+ |
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25 | // |
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26 | /** |
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27 | * This file contains the definition of the Structures_Graph_Manipulator_AcyclicTest graph manipulator. |
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28 | * |
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29 | * @see Structures_Graph_Manipulator_AcyclicTest |
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30 | * @package Structures_Graph |
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31 | */ |
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32 | |
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33 | /* dependencies {{{ */ |
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34 | /** */ |
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35 | require_once 'PEAR.php'; |
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36 | /** */ |
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37 | require_once 'Structures/Graph.php'; |
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38 | /** */ |
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39 | require_once 'Structures/Graph/Node.php'; |
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40 | /* }}} */ |
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41 | |
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42 | /* class Structures_Graph_Manipulator_AcyclicTest {{{ */ |
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43 | /** |
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44 | * The Structures_Graph_Manipulator_AcyclicTest is a graph manipulator |
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45 | * which tests whether a graph contains a cycle. |
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46 | * |
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47 | * The definition of an acyclic graph used in this manipulator is that of a |
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48 | * DAG. The graph must be directed, or else it is considered cyclic, even when |
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49 | * there are no arcs. |
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50 | * |
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51 | * @author Sérgio Carvalho <sergio.carvalho@portugalmail.com> |
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52 | * @copyright (c) 2004 by Sérgio Carvalho |
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53 | * @package Structures_Graph |
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54 | */ |
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55 | class Structures_Graph_Manipulator_AcyclicTest { |
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56 | /* _nonVisitedInDegree {{{ */ |
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57 | /** |
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58 | * |
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59 | * This is a variant of Structures_Graph::inDegree which does |
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60 | * not count nodes marked as visited. |
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61 | * |
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62 | * @access private |
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63 | * @return integer Number of non-visited nodes that link to this one |
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64 | */ |
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65 | function _nonVisitedInDegree(&$node) { |
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66 | $result = 0; |
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67 | $graphNodes =& $node->_graph->getNodes(); |
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68 | foreach (array_keys($graphNodes) as $key) { |
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69 | if ((!$graphNodes[$key]->getMetadata('acyclic-test-visited')) && $graphNodes[$key]->connectsTo($node)) $result++; |
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70 | } |
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71 | return $result; |
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72 | |
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73 | } |
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74 | /* }}} */ |
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75 | |
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76 | /* _isAcyclic {{{ */ |
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77 | /** |
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78 | * @access private |
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79 | */ |
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80 | function _isAcyclic(&$graph) { |
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81 | // Mark every node as not visited |
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82 | $nodes =& $graph->getNodes(); |
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83 | $nodeKeys = array_keys($nodes); |
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84 | $refGenerator = array(); |
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85 | foreach($nodeKeys as $key) { |
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86 | $refGenerator[] = false; |
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87 | $nodes[$key]->setMetadata('acyclic-test-visited', $refGenerator[sizeof($refGenerator) - 1]); |
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88 | } |
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89 | |
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90 | // Iteratively peel off leaf nodes |
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91 | do { |
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92 | // Find out which nodes are leafs (excluding visited nodes) |
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93 | $leafNodes = array(); |
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94 | foreach($nodeKeys as $key) { |
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95 | if ((!$nodes[$key]->getMetadata('acyclic-test-visited')) && Structures_Graph_Manipulator_AcyclicTest::_nonVisitedInDegree($nodes[$key]) == 0) { |
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96 | $leafNodes[] =& $nodes[$key]; |
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97 | } |
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98 | } |
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99 | // Mark leafs as visited |
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100 | for ($i=sizeof($leafNodes) - 1; $i>=0; $i--) { |
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101 | $visited =& $leafNodes[$i]->getMetadata('acyclic-test-visited'); |
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102 | $visited = true; |
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103 | $leafNodes[$i]->setMetadata('acyclic-test-visited', $visited); |
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104 | } |
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105 | } while (sizeof($leafNodes) > 0); |
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106 | |
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107 | // If graph is a DAG, there should be no non-visited nodes. Let's try to prove otherwise |
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108 | $result = true; |
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109 | foreach($nodeKeys as $key) if (!$nodes[$key]->getMetadata('acyclic-test-visited')) $result = false; |
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110 | |
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111 | // Cleanup visited marks |
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112 | foreach($nodeKeys as $key) $nodes[$key]->unsetMetadata('acyclic-test-visited'); |
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113 | |
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114 | return $result; |
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115 | } |
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116 | /* }}} */ |
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117 | |
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118 | /* isAcyclic {{{ */ |
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119 | /** |
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120 | * |
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121 | * isAcyclic returns true if a graph contains no cycles, false otherwise. |
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122 | * |
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123 | * @return boolean true iff graph is acyclic |
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124 | * @access public |
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125 | */ |
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126 | function isAcyclic(&$graph) { |
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127 | // We only test graphs |
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128 | if (!is_a($graph, 'Structures_Graph')) return Pear::raiseError('Structures_Graph_Manipulator_AcyclicTest::isAcyclic received an object that is not a Structures_Graph', STRUCTURES_GRAPH_ERROR_GENERIC); |
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129 | if (!$graph->isDirected()) return false; // Only directed graphs may be acyclic |
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130 | |
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131 | return Structures_Graph_Manipulator_AcyclicTest::_isAcyclic($graph); |
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132 | } |
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133 | /* }}} */ |
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134 | } |
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135 | /* }}} */ |
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136 | ?> |
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