## root / drupal7 / includes / graph.inc @ 6d8023f2

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<?php |
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/** |

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* @file |

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* Directed acyclic graph manipulation. |

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*/ |

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/** |

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* Performs a depth-first search and sort on a directed acyclic graph. |

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* |

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* @param $graph |

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* A three dimensional associated array, with the first keys being the names |

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* of the vertices, these can be strings or numbers. The second key is |

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* 'edges' and the third one are again vertices, each such key representing |

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* an edge. Values of array elements are copied over. |

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* |

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* Example: |

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* @code |

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* $graph[1]['edges'][2] = 1; |

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* $graph[2]['edges'][3] = 1; |

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* $graph[2]['edges'][4] = 1; |

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* $graph[3]['edges'][4] = 1; |

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* @endcode |

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* |

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* On return you will also have: |

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* @code |

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* $graph[1]['paths'][2] = 1; |

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* $graph[1]['paths'][3] = 1; |

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* $graph[2]['reverse_paths'][1] = 1; |

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* $graph[3]['reverse_paths'][1] = 1; |

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* @endcode |

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* |

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* @return |

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* The passed-in $graph with more secondary keys filled in: |

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* - 'paths': Contains a list of vertices than can be reached on a path from |

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* this vertex. |

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* - 'reverse_paths': Contains a list of vertices that has a path from them |

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* to this vertex. |

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* - 'weight': If there is a path from a vertex to another then the weight of |

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* the latter is higher. |

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* - 'component': Vertices in the same component have the same component |

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* identifier. |

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* |

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* @see _drupal_depth_first_search() |

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*/ |

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function drupal_depth_first_search(&$graph) { |

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$state = array( |

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// The order of last visit of the depth first search. This is the reverse |

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// of the topological order if the graph is acyclic. |

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'last_visit_order' => array(), |

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// The components of the graph. |

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'components' => array(), |

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); |

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// Perform the actual search. |

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foreach ($graph as $start => $data) { |

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_drupal_depth_first_search($graph, $state, $start); |

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} |

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// We do such a numbering that every component starts with 0. This is useful |

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// for module installs as we can install every 0 weighted module in one |

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// request, and then every 1 weighted etc. |

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$component_weights = array(); |

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foreach ($state['last_visit_order'] as $vertex) { |

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$component = $graph[$vertex]['component']; |

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if (!isset($component_weights[$component])) { |

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$component_weights[$component] = 0; |

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} |

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$graph[$vertex]['weight'] = $component_weights[$component]--; |

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} |

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} |

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/** |

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* Performs a depth-first search on a graph. |

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* |

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* @param $graph |

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* A three dimensional associated graph array. |

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* @param $state |

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* An associative array. The key 'last_visit_order' stores a list of the |

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* vertices visited. The key components stores list of vertices belonging |

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* to the same the component. |

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* @param $start |

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* An arbitrary vertex where we started traversing the graph. |

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* @param $component |

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* The component of the last vertex. |

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* |

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* @see drupal_depth_first_search() |

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*/ |

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function _drupal_depth_first_search(&$graph, &$state, $start, &$component = NULL) { |

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// Assign new component for each new vertex, i.e. when not called recursively. |

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if (!isset($component)) { |

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$component = $start; |

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} |

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// Nothing to do, if we already visited this vertex. |

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if (isset($graph[$start]['paths'])) { |

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return; |

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} |

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// Mark $start as visited. |

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$graph[$start]['paths'] = array(); |

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// Assign $start to the current component. |

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$graph[$start]['component'] = $component; |

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$state['components'][$component][] = $start; |

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// Visit edges of $start. |

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if (isset($graph[$start]['edges'])) { |

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foreach ($graph[$start]['edges'] as $end => $v) { |

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// Mark that $start can reach $end. |

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$graph[$start]['paths'][$end] = $v; |

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if (isset($graph[$end]['component']) && $component != $graph[$end]['component']) { |

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// This vertex already has a component, use that from now on and |

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// reassign all the previously explored vertices. |

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$new_component = $graph[$end]['component']; |

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foreach ($state['components'][$component] as $vertex) { |

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$graph[$vertex]['component'] = $new_component; |

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$state['components'][$new_component][] = $vertex; |

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} |

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unset($state['components'][$component]); |

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$component = $new_component; |

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} |

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// Only visit existing vertices. |

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if (isset($graph[$end])) { |

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// Visit the connected vertex. |

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_drupal_depth_first_search($graph, $state, $end, $component); |

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// All vertices reachable by $end are also reachable by $start. |

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$graph[$start]['paths'] += $graph[$end]['paths']; |

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} |

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} |

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} |

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// Now that any other subgraph has been explored, add $start to all reverse |

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// paths. |

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foreach ($graph[$start]['paths'] as $end => $v) { |

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if (isset($graph[$end])) { |

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$graph[$end]['reverse_paths'][$start] = $v; |

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} |

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} |

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// Record the order of the last visit. This is the reverse of the |

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// topological order if the graph is acyclic. |

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$state['last_visit_order'][] = $start; |

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} |