Create 01_binary_search.php (#13)

01_introduction_to_algorithms/php/01_binary_search.php

@@ -0,0 +1,26 @@
+<?php
+
+function binarySearch($needle, $array) {
+  $low = 0;
+  $high = count($array) - 1;
+
+  while ($low <= $high) {
+    $middle = floor(($low + $high) / 2);
+
+    if ($array[$middle] == $needle) {
+      return $middle;
+    }
+
+    if ($array[$middle] > $needle) {
+      $high = $middle - 1;
+    } else {
+      $low = $middle + 1;
+    }
+  }
+
+  return null;
+}
+
+$array = [1, 3, 5, 7, 9];
+echo binarySearch(3, $array) . "\n";
+echo binarySearch(-1, $array) . "\n";