Php quick sorting code execution process

The problem is: why are there two arrays, arrayempty and array0 & amp; gt; int6, printed on $ left? It is reasonable to say that after recursively calling the array array0 & amp; gt; int1, the return $ arr of the 71 rows will be executed directly. how can we still have the next two arrays ?...

The problem is as follows:
Why is the array empty and array 0 => int 6 displayed in $ left? It is reasonable to say that after recursively calling the array 0 => int 1, the return $ arr of the 71 rows will be executed directly. how can we still have the next 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 as follows:
Why is the array empty and array 0 => int 6 displayed in $ left? It is reasonable to say that after recursively calling the array 0 => int 1, the return $ arr of the 71 rows will be executed directly. how can we still have the next 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));

Dump is left. If the array is [, 3], it is null, and [, 1] is one.

$ 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 is easier to use this idea.