Merge pull request #94 from andremralves/master

Add non recursive DFS algorithm

DIRECTORY.md

@@ -13,6 +13,9 @@
   * [Octaltodecimal](./Conversions/OctalToDecimal.php)
   * [Speedconversion](./Conversions/SpeedConversion.php)
 
+## Graphs
+  * [DepthFirstSearch](./Graphs/DepthFirstSearch.php)
+
 ## Maths
   * [Absolutemax](./Maths/AbsoluteMax.php)
   * [Absolutemin](./Maths/AbsoluteMin.php)

Graphs/DepthFirstSearch.php

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * The Depth-first Search is an algorithm used for traversing or searching trees or graphs 
+ * (https://en.wikipedia.org/wiki/Depth-first_search).
+ * 
+ * This is a non recursive implementation.
+ * 
+ * References:
+ * https://www.geeksforgeeks.org/depth-first-search-or-dfs-for-a-graph/
+ * 
+ * https://the-algorithms.com/algorithm/depth-first-search?lang=python
+ * 
+ * @author Andre Alves https://github.com/andremralves
+ * @param array $adjList An array representing the grapth as an Adjacent List
+ * @param int|string $start The starting vertex
+ * @return array The visited vertices 
+ */
+function dfs($adjList, $start)
+{
+    $visited = [];
+    $stack = [$start];
+    while (!empty($stack)) {
+        // Removes the ending element from the stack and mark as visited
+        $v = array_pop($stack);
+        $visited[$v] = 1;
+
+        // Checks each adjacent vertex of $v and add to the stack if not visited
+        foreach (array_reverse($adjList[$v]) as $adj) {
+            if (!array_key_exists($adj, $visited))
+                array_push($stack, $adj);
+        }
+    }
+    return array_keys($visited);
+}

tests/Graphs/DepthFirstSearchTest.php

@@ -0,0 +1,48 @@
+<?php
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+require_once __DIR__ . '/../../Graphs/DepthFirstSearch.php';
+
+use PHPUnit\Framework\TestCase;
+
+class DepthFirstSearchTest extends TestCase
+{
+    public function testDepthFirstSearch()
+    {
+        $graph = array(
+            "A" => ["B", "C", "D"],
+            "B" => ["A", "D", "E"],
+            "C" => ["A", "F"],
+            "D" => ["B", "D"],
+            "E" => ["B", "F"],
+            "F" => ["C", "E", "G"],
+            "G" => ["F"],
+        );
+        $visited = dfs($graph, "A");
+        $this->assertEquals(["A", "B", "D", "E", "F", "C", "G"], $visited);
+    }
+    public function testDepthFirstSearch2()
+    {
+        $graph = array(
+            [1, 2],
+            [2],
+            [0, 3],
+            [3],
+        );
+
+        $visited = dfs($graph, 2);
+        $this->assertEquals([2, 0, 1, 3], $visited);
+    }
+    public function testDepthFirstSearch3()
+    {
+        $graph = array(
+            [2, 3, 1],
+            [0],
+            [0, 4],
+            [0],
+            [2],
+        );
+        $visited = dfs($graph, 0);
+        $this->assertEquals([0, 2, 4, 3, 1], $visited);
+    }
+}