快速排序

$arr=array(33,2,54,25,65,34,67,42,87,90,243,213,365,78,67,345,678);

function quick_sort($arr){ 
    $len = count($arr); 
    if($len <= 1) 
    { 
        return $arr; 
    } 
    $key = $arr[0]; 
    $arr_left = array(); 
    $arr_right = array(); 
    for ($i=1;$i<$len;$i++) 
    { 
        if($arr[$i] <= $key){ 
            $arr_left[] = $arr[$i]; 
        }else{ 
            $arr_right[] = $arr[$i]; 
        } 
    } 
    $arr_left = quick_sort($arr_left); 
    $arr_right = quick_sort($arr_right); 
    return array_merge($arr_left,array($key),$arr_right); 
}

echo '<pre>';
print_r(quick_sort($arr));
echo '</pre>';