public function run(string $file, Node $node): array
    {
        $hints = [];
        $keys = [];

        foreach ($node->children as $elem) {
            if (is_null($elem)) {
                continue;
            }

            $key = $elem->children['key'];
            // If the array does not have key, ignores this element.
            if (!is_null($key)) {
                foreach ($keys as $other_key) {
                    if ($this->isEqualsWithoutLineno($key, $other_key)) {
                        $hints[] = new Hint(
                            self::HINT_TYPE,
                            self::HINT_MESSAGE,
                            $file,
                            $elem->lineno,
                            self::HINT_LINK
                        );
                    }
                }
                $keys[] = $key;
            }
        }

        return $hints;
    }