@array = ("NULL","NULL",1,3,70,"NULL","NULL","NULL","NULL",
	     "NULL",50,1,"NULL",4,"NULL","NULL",5,"NULL","NULL","NULL");
$max_element = @array - 1;
for $i (0 .. @array-1)
{
    if($array[$i] eq "NULL")
    {
	$left_i = $i-1;
	$right_i = $i;
	#find the index of the next non null (but the array might end on a null)
	while($array[$right_i] eq "NULL" && $right_i<=$max_element) 
	{
	    $right_i++;
	}
	if($right_i > $max_element) 
	{
	    #if the array ends with nulls then just replace them all w/ $array[$left_i]
	    for $null_index ($i .. $max_element)
	    {
		$array[$null_index] = $array[$left_i];
	    }
	    $i = $max_element;
	}
	elsif($left_i < 0)
	{
	    #if the array starts with nulls then just replace all with $array[$right_i]
	    for $null_index ($i .. $right_i - 1)
	    {
		$array[$null_index] = $array[$right_i];
	    }
	    $i=$right_i;
	}
	else
	{
	    for $null_index ($i .. $right_i-1)
	    {
		if($null_index - $left_i  == $right_i - $null_index)
		{
		    $array[$null_index] = ($array[$left_i] + $array[$right_i])/2;
		}
		if($null_index - $left_i > $right_i - $null_index)
		{
		    $array[$null_index] = $array[$right_i];
		}
		if($null_index - $left_i < $right_i - $null_index)
		{
		    $array[$null_index] = $array[$left_i];
		}
	    }
	    $i=$right_i;
	}
    }
}
for $ar (@array)
{
    print $ar . " ";
}
print "\n";
#OUTPUT
#1 1 1 3 70 70 70 60 50 50 50 1 2.5 4 4 5 5 5 5 5