PHP快速排序

function quick_sort($arr) {
$cnt = count($arr);
if($cnt <= 1) {
return $arr;
}
$base_num    = $arr[0];
$left_array  = array();
$right_array = array();
for($i = 1; $i < $cnt; $i++) {
if($base_num > $arr[$i]) {
$left_array[] = $arr[$i];
} else {
$right_array[] = $arr[$i];
}
}
$left_array  = quick_sort($left_array);
$right_array = quick_sort($right_array);
return array_merge($left_array, array($base_num), $right_array);
}
echo '<pre>';
var_dump(quick_sort($arr));