use strict;
use warnings;
use Data::Dumper;
# Read the data from the file...
#
my @lines = map { chomp; [split] } ;
# Arrays are indexed from 0, but we want to count lines
# from 1, so let's unshift a dummy 0 entry onto the array.
#
unshift @lines, undef;
# This is a more usual way of implementing "uniq". It
# preserves the original input order.
#
sub uniq
{
my %seen;
grep { not $seen{$_}++ } @_;
}
# This is the function that does most of the work. It
# calculates what graph theorists would call a "closure"
# over the graph of line references.
#
sub line_closure
{
# We're given an input list, which is a set of
# lines already in the closure.
#
my @input = @_;
# Extend the list by looping through @input to
# generate the output.
#
my @output = uniq map {
# if the line referred to exists
$lines[$_]
# then add the numbers from that
# line
? ($_, @{$lines[$_]})
# otherwise, just keep the existing
# number
: ($_)
} @input;
# If the two lists match (and because we're only
# ever adding to the list, checking the list
# lengths is sufficient), then we've found the
# closure, so return it.
#
if (@output == @input)
{
return @output;
}
# Otherwise, calculate the closure on the expanded
# list.
#
return line_closure(@output);
}
# Get the closure starting at line 1.
#
my @results = line_closure(1);
print Dumper \@results;
__DATA__
1 2 4
2 3 4
3 7
4 6
5 10 11 12 13
6
7 1