protected function Graph::depthFirstSearch in Drupal 8

Same name and namespace in other branches

9 core/lib/Drupal/Component/Graph/Graph.php \Drupal\Component\Graph\Graph::depthFirstSearch()
10 core/lib/Drupal/Component/Graph/Graph.php \Drupal\Component\Graph\Graph::depthFirstSearch()

Performs a depth-first search on a graph.

Parameters

$state: An associative array. The key 'last_visit_order' stores a list of the vertices visited. The key components stores list of vertices belonging to the same the component.

$start: An arbitrary vertex where we started traversing the graph.

$component: The component of the last vertex.

File

core/lib/Drupal/Component/Graph/Graph.php, line 101

Class

Graph: Directed acyclic graph manipulation.

Namespace

Drupal\Component\Graph

Code

protected function depthFirstSearch(&$state, $start, &$component = NULL) {

  // Assign new component for each new vertex, i.e. when not called recursively.
  if (!isset($component)) {
    $component = $start;
  }

  // Nothing to do, if we already visited this vertex.
  if (isset($this->graph[$start]['paths'])) {
    return;
  }

  // Mark $start as visited.
  $this->graph[$start]['paths'] = [];

  // Assign $start to the current component.
  $this->graph[$start]['component'] = $component;
  $state['components'][$component][] = $start;

  // Visit edges of $start.
  if (isset($this->graph[$start]['edges'])) {
    foreach ($this->graph[$start]['edges'] as $end => $v) {

      // Mark that $start can reach $end.
      $this->graph[$start]['paths'][$end] = $v;
      if (isset($this->graph[$end]['component']) && $component != $this->graph[$end]['component']) {

        // This vertex already has a component, use that from now on and
        // reassign all the previously explored vertices.
        $new_component = $this->graph[$end]['component'];
        foreach ($state['components'][$component] as $vertex) {
          $this->graph[$vertex]['component'] = $new_component;
          $state['components'][$new_component][] = $vertex;
        }
        unset($state['components'][$component]);
        $component = $new_component;
      }

      // Only visit existing vertices.
      if (isset($this->graph[$end])) {

        // Visit the connected vertex.
        $this
          ->depthFirstSearch($state, $end, $component);

        // All vertices reachable by $end are also reachable by $start.
        $this->graph[$start]['paths'] += $this->graph[$end]['paths'];
      }
    }
  }

  // Now that any other subgraph has been explored, add $start to all reverse
  // paths.
  foreach ($this->graph[$start]['paths'] as $end => $v) {
    if (isset($this->graph[$end])) {
      $this->graph[$end]['reverse_paths'][$start] = $v;
    }
  }

  // Record the order of the last visit. This is the reverse of the
  // topological order if the graph is acyclic.
  $state['last_visit_order'][] = $start;
}

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