shell排序

function shell_sort(&$arr)
{
         if(!is_array($arr)) return;
        $n = count($arr);
        for($gap=floor($n/2);$gap>0;$gap=floor($gap/=2))
        {
                for($i=$gap;$i<$n;++$i)
                {
                        for($j=$i-$gap;$j>=0&&$arr[$j+$gap]<$arr[$j];$j-=$gap)
                        {
                                $temp = $arr[$j];
                                $arr[$j] = $arr[$j+$gap];
                                $arr[$j+$gap] = $temp;

                    }

              }

        }

}