Created
September 1, 2012 00:14
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Topological sorting with directed cycle detection
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<?php | |
$a = new Node('a'); | |
$b = new Node('b'); | |
$c = new Node('c'); | |
$d = new Node('d'); | |
$e = new Node('e'); | |
$a->dependsOn($b); | |
$a->dependsOn($d); | |
$b->dependsOn($c); | |
$b->dependsOn($e); | |
$c->dependsOn($d); | |
$c->dependsOn($e); | |
$d->dependsOn($b); | |
$resolved = resolveDependency($a); | |
foreach ($resolved as $resolvedNode) { | |
echo $resolvedNode->getName() . PHP_EOL; | |
} | |
function resolveDependency(Node $node, &$resolved = array(), &$seen = array()) { | |
$seen[] = $node; | |
foreach ($node->getEdges() as $edge) { | |
if (!in_array($edge, $resolved)) { | |
if (!in_array($node, $seen)) { | |
resolveDependency($edge, $resolved); | |
} | |
else { | |
throw new RuntimeException('Circular reference detected!'); | |
} | |
} | |
} | |
$resolved[] = $node; | |
return $resolved; | |
} | |
class Node | |
{ | |
private $name; | |
private $edges = array(); | |
public function __construct($name) | |
{ | |
$this->name = $name; | |
} | |
public function dependsOn(Node $node) | |
{ | |
$this->edges[] = $node; | |
} | |
public function getName() | |
{ | |
return $this->name; | |
} | |
public function getEdges() | |
{ | |
return $this->edges; | |
} | |
} |
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