Move Set directed helpers to new Algorithm\Directed

Author: clue

src/Directed.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Fhaculty\Graph\Algorithm;
+
+use Fhaculty\Graph\Set;
+use Fhaculty\Graph\Algorithm\Base;
+use Fhaculty\Graph\Edge\Directed as EdgeDirected;
+
+class Directed extends Base
+{
+    private $set;
+
+    public function __construct(Set $graphOrWalk)
+    {
+        $this->set = $graphOrWalk;
+    }
+
+    /**
+     * checks whether the graph has any directed edges (aka digraph)
+     *
+     * @return boolean
+     */
+    public function isDirected()
+    {
+        foreach ($this->set->getEdges() as $edge) {
+            if ($edge instanceof EdgeDirected) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

src/MaximumMatching/Flow.php

@@ -2,6 +2,8 @@
 
 namespace Fhaculty\Graph\Algorithm\MaximumMatching;
 
+use Fhaculty\Graph\Algorithm\Directed;
+
 use Fhaculty\Graph\Exception\LogicException;
 
 use Fhaculty\Graph\Exception\UnexpectedValueException;
@@ -14,7 +16,8 @@ class Flow extends Base
 {
     public function getEdges()
     {
-        if ($this->graph->isDirected()) {
+        $alg = new Directed($this->graph);
+        if ($alg->isDirected()) {
             throw new UnexpectedValueException('Input graph contains directed edges');
         }