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add isAcyclic function in the GraphProperty class #38

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add isAcyclic function in the GraphProperty class #38

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70bd7d6
add isAcyclic function in the GraphProperty class to check wether a g…
Gillu13 Jan 29, 2020
b2fb6a8
change array GraphProperty/isAcyclic (PHP 5.3 compliance)
Gillu13 Jan 30, 2020
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43 changes: 43 additions & 0 deletions src/Property/GraphProperty.php
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Original file line number Diff line number Diff line change
Expand Up @@ -48,4 +48,47 @@ public function isTrivial()
{
return ($this->graph->getEdges()->isEmpty() && \count($this->graph->getVertices()) === 1);
}

/**
* checks whether this graph is acyclic (directed graph with no cycles)
* using the Kahn algorithm
*
* @return boolean
* @link https://en.wikipedia.org/wiki/Directed_acyclic_graph
*/
public function isAcyclic()
{
$vertices = $this->graph->getVertices();
$nVertices = count($vertices);
$visited = 0;
$inDegree = array();
$stack = array();

foreach($vertices as $vert){
$deg=count($vert->getEdgesIn());
$inDegree[$vert->getId()]=$deg;
if($deg==0){
\array_push($stack,$vert);
}
}

while(!(empty($stack))){
$n = array_pop($stack);
$visited++;
foreach($n->getEdgesOut() as $e){
$m = $e->getVertexEnd();
$inDegree[$m->getId()]--;
if($inDegree[$m->getId()]==0){
\array_push($stack,$m);
}
}
}

if($visited==$nVertices){
return true;
}
else{
return false;
}
}
}
46 changes: 46 additions & 0 deletions tests/Property/PropertyGraphTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ public function testEmptyIsEdgeless()
$this->assertTrue($alg->isNull());
$this->assertTrue($alg->isEdgeless());
$this->assertFalse($alg->isTrivial());
$this->assertTrue($alg->isAcyclic());
}

public function testSingleVertexIsTrivial()
Expand All @@ -26,5 +27,50 @@ public function testSingleVertexIsTrivial()
$this->assertFalse($alg->isNull());
$this->assertTrue($alg->isEdgeless());
$this->assertTrue($alg->isTrivial());
$this->assertTrue($alg->isAcyclic());
}

public function testUndirectedIsAcyclic()
{
$graph = new Graph();
$graph->createVertex(1)->createEdge($graph->createVertex(2));

$alg = new GraphProperty($graph);

$this->assertFalse($alg->isNull());
$this->assertFalse($alg->isEdgeless());
$this->assertFalse($alg->isTrivial());
$this->assertFalse($alg->isAcyclic());
}

public function testGraphSimpleIsAcyclic()
{
$graph = new Graph();
$graph->createVertex(1)->createEdgeTo($graph->createVertex(2));

$alg = new GraphProperty($graph);

$this->assertFalse($alg->isNull());
$this->assertFalse($alg->isEdgeless());
$this->assertFalse($alg->isTrivial());
$this->assertTrue($alg->isAcyclic());
}

public function testGraphWithCycleIsAcyclic()
{
$graph = new Graph();
$vertexOne = $graph->createVertex(1);
$vertexTwo = $graph->createVertex(2);
$vertexThree = $graph->createVertex(3);
$vertexOne->createEdgeTo($vertexTwo);
$vertexTwo->createEdgeTo($vertexThree);
$vertexThree->createEdgeTo($vertexOne);

$alg = new GraphProperty($graph);

$this->assertFalse($alg->isNull());
$this->assertFalse($alg->isEdgeless());
$this->assertFalse($alg->isTrivial());
$this->assertFalse($alg->isAcyclic());
}
}