php example of breadth-firsth search (#58)

06_breadth-first_search/php/01_breadth-first_search.php

@@ -0,0 +1,46 @@
+<?php
+
+function personIsSeller(string $name): bool {
+    return $name[-1] == "m";
+}
+
+$graph = [];
+$graph["you"] = ["alice", "bob", "claire"];
+$graph["bob"] = ["anuj", "peggy"];
+$graph["alice"] = ["peggy"];
+$graph["claire"] = ["thom", "jonny"];
+$graph["anuj"] = [];
+$graph["peggy"] = [];
+$graph["thom"] = [];
+$graph["jonny"] = [];
+
+function enqueue(\SplQueue $queue, array $persons) {
+    foreach ($persons as $person) {
+        $queue->enqueue($person);
+    }
+}
+
+function search(string $name): bool {
+    global $graph;
+    $searchQueue = new \SplQueue();
+    enqueue($searchQueue, $graph[$name]);
+    # This array is how you keep track of which people you've searched before.
+    $searched = [];
+    while (!$searchQueue->isEmpty()) {
+        $person = $searchQueue->dequeue();
+        # Only search this person if you haven't already searched them.
+        if (!isset($searched[$person])) {
+            if (personIsSeller($person)) {
+                printf("%s is a mango seller", $person);
+                return true;
+            } else {
+                enqueue($searchQueue, $graph[$person]);
+                # Marks this person as searched
+                $searched[$person] = true;
+            }
+        }
+    }
+    return false;
+}
+
+search("you");