Merge remote-tracking branch 'origin/add-algo-tree'

Conflicts:
	CHANGELOG.md

Author: clue

src/Tree/Base.php

@@ -0,0 +1,88 @@
+<?php
+
+namespace Fhaculty\Graph\Algorithm\Tree;
+
+use Fhaculty\Graph\Algorithm\BaseGraph;
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Vertex;
+use Fhaculty\Graph\Exception\UnderflowException;
+use Fhaculty\Graph\Exception\UnexpectedValueException;
+use Fhaculty\Graph\Algorithm\Search\StrictDepthFirst;
+
+/**
+ * Abstract base class for tree algorithms
+ *
+ * This abstract base class provides the base interface for working with
+ * graphs that represent a tree.
+ *
+ * A tree is a connected Graph (single component) with no cycles. Every Tree is
+ * a Graph, but not every Graph is a Tree.
+ *
+ *    A
+ *   / \
+ *  B   C
+ *     / \
+ *    D   E
+ *
+ * Special cases are undirected trees (like the one pictured above), handled via
+ * Tree\Undirected and directed, rooted trees (InTree and OutTree), handled via
+ * Tree\BaseDirected.
+ *
+ * @link http://en.wikipedia.org/wiki/Tree_%28graph_theory%29
+ * @link http://en.wikipedia.org/wiki/Tree_%28data_structure%29
+ * @see Undirected for an implementation of these algorithms on (undirected) trees
+ * @see BaseDirected for an abstract implementation of these algorithms on directed, rooted trees
+ */
+abstract class Base extends BaseGraph
+{
+    /**
+     * checks whether the given graph is actually a tree
+     *
+     * @return boolean
+     */
+    abstract public function isTree();
+
+    /**
+     * checks if the given $vertex is a leaf (outermost vertext)
+     *
+     * leaf vertex is also known as leaf node, external node or terminal node
+     *
+     * @param Vertex $vertex
+     * @return boolean
+     */
+    abstract public function isVertexLeaf(Vertex $vertex);
+
+    /**
+     * checks if the given $vertex is an internal vertex (somewhere in the "middle" of the tree)
+     *
+     * internal vertex is also known as inner node (inode) or branch node
+     *
+     * @param Vertex $vertex
+     * @return boolean
+     */
+    abstract public function isVertexInternal(Vertex $vertex);
+
+    /**
+     * get array of leaf vertices (outermost vertices with no children)
+     *
+     * @return Vertex[]
+     * @uses Graph::getVertices()
+     * @uses self::isVertexLeaf()
+     */
+    public function getVerticesLeaf()
+    {
+        return array_filter($this->graph->getVertices(), array($this, 'isVertexLeaf'));
+    }
+
+    /**
+     * get array of internal vertices
+     *
+     * @return Vertex[]
+     * @uses Graph::getVertices()
+     * @uses self::isVertexInternal()
+     */
+    public function getVerticesInternal()
+    {
+        return array_filter($this->graph->getVertices(), array($this, 'isVertexInternal'));
+    }
+}