function mergesort($arr){
	if(count($arr) == 1 ) return $arr;
	$mid = count($arr) / 2;
    $left = array_slice($arr, 0, $mid);
    $right = array_slice($arr, $mid);
	$left = mergesort($left);
	$right = mergesort($right);
	return merge($left, $right);
}

function merge($left, $right){
	$res = array();
	while (count($left) > 0 && count($right) > 0){
		if($left[0] > $right[0]){
			$res[] = $right[0];
			$right = array_slice($right , 1);
		}else{
			$res[] = $left[0];
			$left = array_slice($left, 1);
		}
	}
	while (count($left) > 0){
		$res[] = $left[0];
		$left = array_slice($left, 1);
	}
	while (count($right) > 0){
		$res[] = $right[0];
		$right = array_slice($right, 1);
	}
	return $res;
}

$arr = array( 1, 5, 2, 7, 3, 9, 4, 6, 8);
$arr = mergesort($arr);
echo implode(',',$arr);