PHP实现快速排序算法

<?php
 
function quicksort($seq) {
 
  if (count($seq) > 1) {
 
    $k = $seq[0];
 
    $x = array();
 
    $y = array();
 
    for ($i=1; $i<count($seq); $i++) {
 
      if ($seq[$i] <= $k) {
 
        $x[] = $seq[$i];
 
      } else {
 
        $y[] = $seq[$i];
 
      }
 
    }
 
    $x = quicksort($x);
 
    $y = quicksort($y);
 
    return array_merge($x, array($k), $y);
 
  } else {
 
    return $seq;
 
  }
 
}
 
  
 
$arr = array(12,2,16,30,8,28,4,10,20,6,18);
 
print_r(quicksort($arr));
 
?>