<?php

function quickSort(&$arr){

if(count($arr)>1){

$k=$arr[0];

$x=array();

$y=array();

$_size=count($arr);

for($i=1;$i<$_size;$i++){

if($arr[$i]<=$k){

$x[]=$arr[$i];

}else{

$y[]=$arr[$i];

}

}

echo implode(', ',$x). PHP_EOL;

echo implode(', ',$y). PHP_EOL;

$x=quickSort($x);

$y=quickSort($y);

return array_merge($x,array($k),$y);

}else{

return $arr;

}

}

$test_array = array(49, 40, 60, 80, 30, 70, 90, 10, 50, 0);

echo implode(', ',quickSort($test_array)). PHP_EOL;

//https://codereview.stackexchange.com/questions/82834/quick-sort-in-php

//https://pageconfig.com/post/implementing-quicksort-in-php