Questions about the PHP Quick Sort Code Execution process

The problem is this:
Why does this print $left have array empty, array 0, and int 6 appear? Logically, recursive calls to array 0 + int 1 after the array is executed directly after the return of the 71 line $arr Ah, how can there be two arrays?

The source code is as follows:

$arr = array(6,3,8,6,4,2,9,5,1);function quick_sort($arr){    if(!is_array($arr)) return false;        $length = count($arr);    if($length <= 1) return $arr;    $left = $right = array();    for($i = 1;$i < $length;$i++){                                                        if($arr[$i] < $arr[0]){            $left[] = $arr[$i];                                     }else{            $right[] = $arr[$i];                                               }    }    var_dump($left);    $left = quick_sort($left);    $right = quick_sort($right);    return array_merge($left,array($arr[0]),$right);}print_r(quick_sort($arr));

Reply content:

The problem is this:
Why does this print $left have array empty, array 0, and int 6 appear? Logically, recursive calls to array 0 + int 1 after the array is executed directly after the return of the 71 line $arr Ah, how can there be two arrays?

The source code is as follows:

$arr = array(6,3,8,6,4,2,9,5,1);function quick_sort($arr){    if(!is_array($arr)) return false;        $length = count($arr);    if($length <= 1) return $arr;    $left = $right = array();    for($i = 1;$i < $length;$i++){                                                        if($arr[$i] < $arr[0]){            $left[] = $arr[$i];                                     }else{            $right[] = $arr[$i];                                               }    }    var_dump($left);    $left = quick_sort($left);    $right = quick_sort($right);    return array_merge($left,array($arr[0]),$right);}print_r(quick_sort($arr));

You dump is left, if the array is [1,3,3] is empty ah, [2,3,1] is a AH

$arr = Array (6,3,8,6,4,2,9,5,1);
$result = Array ();
function aaa ($arr, $result) {

$min = min($arr);array_push($result, $min);$key=array_search($min ,$arr);array_splice($arr,$key,1);if(count($arr)){    aaa($arr,$result);}else{    echo json_encode($result);    exit;}

}
AAA ($arr, $result);

It feels easier with this idea.

