quicksort.php

<?php

function quicksort(Array $array) {
  if (count($array) <= 1) return $array;
  $p = current($array);
  $less = array_filter($array, function($n) use ($p) { return $n < $p; });
  $greater = array_filter($array, function($n) use ($p) { return $n > $p; });  
  return array_merge(quicksort($less), [$p], quicksort($greater));
}

print_r(quicksort([123, 12, 65, 87, 9, 90, 91, 50, 24]));

/*
Array
(
    [0] => 9
    [1] => 12
    [2] => 24
    [3] => 50
    [4] => 65
    [5] => 87
    [6] => 90
    [7] => 91
    [8] => 123
)
[Finished in 0.4s]
*/