PHP algorithm for Shaker Sort / Cocktail Sort with test

Author: Djuki

sort/shaker_sort/php/shaker_sort.php

@@ -0,0 +1,48 @@
+<?php
+
+    function loop_replacing($start, $end, $items, $i) {
+        // Replace elements
+        $forward_is_lighter = $start < $end && $items[$start] > $items[$i];
+        $backward_is_heavier = $start > $end && $items[$start] < $items[$i];
+
+        if ($forward_is_lighter || $backward_is_heavier) {
+            $temp = $items[$start];
+            $items[$start] = $items[$i];
+            $items[$i] = $temp;
+            unset($temp);
+        }
+        return $items;
+    }
+
+    function shaker_sort($input) {
+        $items = count($input) - 1;
+
+        $start = 0;
+        $end = $items;
+        while ($start !== $end) {
+            if ($start < $end) {
+                // Loop forward
+                for ($i = $start; $i <= $end; $i++) {
+                    $input = loop_replacing($start, $end, $input, $i);
+                }
+                // Reduce next looping
+                $start++;
+            } else {
+                // Loop backward
+                for ($i = $start; $i >= $end; $i--) {
+                    $input = loop_replacing($start, $end, $input, $i);
+                }
+                // Reduce next looping
+                $start--;
+            }
+            
+            // Switch start and end to revert moving through array
+            $temp = $end;
+            $end = $start;
+            $start = $temp;
+            unset($temp);
+
+        }
+
+        return $input;
+    }

sort/shaker_sort/php/shaker_sort_test.php

@@ -0,0 +1,10 @@
+<?php
+
+include "shaker_sort.php";
+
+$array = [42, 5, 89, 2, 44, 0, 23, -2, 109, 76, 19, -6, 99, 98];
+$sorted = shaker_sort($array);
+
+$expected = [-6, -2, 0, 2, 5, 19, 23, 42, 44, 76, 89, 98, 99, 109];
+echo ($expected == $sorted) ? 'Array is sorted !!' : 'Array is not sorted as expected';
+var_dump('array', $array, 'sorted set', $sorted);