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<?php |
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namespace TemplesOfCode\NodesAndEdges\DFS; |
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use TemplesOfCode\NodesAndEdges\Graph; |
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/** |
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* Class DirectedCycle |
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* @package TemplesOfCode\NodesAndEdges\DFS |
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*/ |
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class DirectedCycle extends ConnectedComponent |
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{ |
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/** |
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* @var array |
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*/ |
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protected $onStack; |
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/** |
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* @var array |
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*/ |
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protected $cycle; |
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/** |
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* @var int[] |
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*/ |
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private $edgeTo; |
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/** |
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* DirectedCycle constructor. |
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* @param Graph $graph |
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*/ |
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public function __construct(Graph $graph) |
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{ |
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// set |
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$vertices = $graph->getVertices(); |
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// set |
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$this->onStack = array_fill(0, $vertices, false); |
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// init |
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$this->cycle = null; |
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// set |
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$this->graph = $graph; |
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// set |
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$this->marked = array_fill(0, $vertices, false); |
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// iterate over the vertices |
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for ($vertex = 0; $vertex < $vertices; $vertex++) { |
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// check for visit |
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if (!$this->marked[$vertex]) { |
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// execute DFS logic |
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$this->dfs($vertex); |
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} |
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} |
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} |
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/** |
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* @param int $vertex |
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*/ |
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protected function dfs(int $vertex) |
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{ |
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// mark the visit |
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$this->marked[$vertex] = true; |
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// set stack presence |
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$this->onStack[$vertex] = true; |
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// get neighbors |
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$neighbors = $this->graph->adjacent($vertex); |
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// iterate over the set |
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foreach ($neighbors as $w) { |
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// check for cycles |
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if ($this->hasCycle()) { |
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// cycle detected |
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return; |
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} elseif (!$this->marked[$w]) { |
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// set |
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$this->edgeTo[$w] = $vertex; |
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// we have not visited yet |
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$this->dfs($w); |
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} elseif ($this->onStack[$w]) { |
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// we are currently in a path that has visited $w |
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$this->cycle = []; |
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// iterate over the path |
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for ($x = $vertex; $x != $w; $x = $this->edgeTo[$x]) { |
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// add to the end of the list |
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array_unshift($this->cycle, $x); |
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} |
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// stack the neighbor |
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array_unshift($this->cycle, $w); |
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// stack the vertex |
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array_unshift($this->cycle, $vertex); |
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} |
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} |
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// remove the stack presence |
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$this->onStack[$vertex] = false; |
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} |
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/** |
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* @return bool |
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*/ |
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public function hasCycle() |
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{ |
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return !is_null($this->cycle); |
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} |
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/** |
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* @return array|null |
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*/ |
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public function cycle() |
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{ |
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return $this->cycle; |
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} |
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} |
templesofcode /
nodes-and-edges
