use strict;
use warnings;
use feature 'say';


my %nodes = ();
for my $line (<DATA>) {
	my $node = Node->new($line, \%nodes); # funktioniert nur, wenn die nodes, auf die verwiesen wird schon da sind
	$nodes{$node->id} = $node;
}

for my $node (values %nodes) {
	say $node->id.': '.join(', ', $node->elements);
}

{
	package Node;

	sub _node_id {
		my $node_ref_str = shift;
		if ($node_ref_str =~ /\[(.+)\]/) {
			return $1;
		}
		else {
			return undef;
		}
	}

	sub new {
		my $class = shift;
		my $str = shift;
		my $nodes = shift;
		
		my ($id, $left_str, $right_str) = $str =~ /\[(\d+)\]: (\[?\w+\]?), (\[?\w+\]?)/;

		my $left = _node_id($left_str) ? $nodes->{_node_id($left_str)} : $left_str;
		my $right = _node_id($right_str) ? $nodes->{_node_id($right_str)} : $right_str;
		my $self = { id => $id, left => $left, right => $right };
		
		bless $self, $class;
		return $self; 
	}

	sub id {
		my $self = shift;
		return $self->{id};
	}

	sub elements {
		my $self = shift;
		
		my @elements = ();
		for ('left', 'right') {
			if ($self->{$_}->isa('Node')) {
				push @elements, $self->{$_}->elements;
			}
			else {
				push @elements, $self->{$_};
			}
		}

		return @elements;
	}

}
__DATA__
[1]: a, b
[2]: c, [1]
[3]: d, e
[4]: f, [3]
[5]: g, h
[6]: i, [5]
[7]: [2], [4]
[8]: j, [6]
[9]: [7], [8]