Move to src-php to make room for Go

src-php/Utils/Arr.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace trizz\AdventOfCode\Utils;
+
+final class Arr
+{
+    /**
+     * Flatten a multi-dimensional array into a single level.
+     *
+     * Based on:
+     *
+     * @see https://github.com/laravel/framework/blob/c16367a1af68d8f3a1addc1a819f9864334e2c66/src/Illuminate/Collections/Arr.php#L221-L249
+     *
+     * @param array<mixed> $array
+     *
+     * @return array<mixed>
+     */
+    public static function flatten(iterable $array, float|int $depth = INF): array
+    {
+        $result = [];
+
+        foreach ($array as $item) {
+            if (!is_array($item)) {
+                $result[] = $item;
+            } else {
+                $values = $depth === 1
+                    ? array_values($item)
+                    : self::flatten($item, $depth - 1);
+
+                foreach ($values as $value) {
+                    $result[] = $value;
+                }
+            }
+        }
+
+        return $result;
+    }
+}