Move Graph::isSymmetric() to new Algorithm\Symmetric

Author: clue

src/Symmetric.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace Fhaculty\Graph\Algorithm;
+
+use Fhaculty\Graph\Edge\Directed as EdgeDirected;
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Vertex;
+
+class Symmetric extends Base
+{
+    /**
+     *
+     * @var Graph
+     */
+    private $graph;
+
+    public function __construct(Graph $graph)
+    {
+        $this->graph = $graph;
+    }
+
+    /**
+     * checks whether this graph is symmetric (for every edge a->b there's also an edge b->a)
+     *
+     * @return boolean
+     * @uses Graph::getEdges()
+     * @uses EdgeDirected::getVertexStart()
+     * @uses EdgeDirected::getVertedEnd()
+     * @uses Vertex::hasEdgeTo()
+     */
+    public function isSymmetric()
+    {
+        // check all edges
+        foreach ($this->graph->getEdges() as $edge) {
+            // only check directed edges (undirected ones are symmetric by definition)
+            if ($edge instanceof EdgeDirected) {
+                // check if end also has an edge to start
+                if (!$edge->getVertexEnd()->hasEdgeTo($edge->getVertexStart())) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+}