Actualización

vendor/graphp/algorithms/src/DetectNegativeCycle.php

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+<?php
+
+namespace Graphp\Algorithms;
+
+use Fhaculty\Graph\Exception\NegativeCycleException;
+use Fhaculty\Graph\Exception\UnderflowException;
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Walk;
+use Graphp\Algorithms\ShortestPath\MooreBellmanFord as SpMooreBellmanFord;
+
+class DetectNegativeCycle extends BaseGraph
+{
+    /**
+     * check if the input graph has any negative cycles
+     *
+     * @return bool
+     * @uses AlgorithmDetectNegativeCycle::getCycleNegative()
+     */
+    public function hasCycleNegative()
+    {
+        try {
+            $this->getCycleNegative();
+
+            // cycle was found => okay
+            return true;
+        // no cycle found
+        } catch (UnderflowException $ignore) {}
+
+        return false;
+    }
+
+    /**
+     * Searches all vertices for the first negative cycle
+     *
+     * @return Walk
+     * @throws UnderflowException if there's no negative cycle
+     * @uses AlgorithmSpMooreBellmanFord::getVertices()
+     */
+    public function getCycleNegative()
+    {
+        // remember vertices already visited, as they can not lead to a new cycle
+        $verticesVisited = array();
+        // check for all vertices
+        foreach ($this->graph->getVertices()->getMap() as $vid => $vertex) {
+            // skip vertices already visited
+            if (!isset($verticesVisited[$vid])) {
+                // start MBF algorithm on current vertex
+                $alg = new SpMooreBellmanFord($vertex);
+
+                try {
+                    // try to get all connected vertices (or throw new cycle)
+                    foreach ($alg->getVertices()->getIds() as $vid) {
+                        // getting connected vertices succeeded, so skip over all of them
+                        $verticesVisited[$vid] = true;
+                    // no cycle found, check next vertex...
+                    }
+                // yey, negative cycle encountered => return
+                } catch (NegativeCycleException $e) {
+                    return $e->getCycle();
+                }
+            }
+        // no more vertices to check => abort
+        }
+        throw new UnderflowException('No negative cycle found');
+    }
+
+    /**
+     * create new graph clone with only vertices and edges in negative cycle
+     *
+     * @return Graph
+     * @throws UnderflowException if there's no negative cycle
+     * @uses AlgorithmDetectNegativeCycle::getCycleNegative()
+     * @uses Walk::createGraph()
+     */
+    public function createGraph()
+    {
+        return $this->getCycleNegative()->createGraph();
+    }
+}