use strict;

my %hash;
while (<DATA>){
	chomp;
	my @array = split(',',$_);
	my ($child, $parent) = ($2,$1);
	$hash{$array[1]} = [] unless (exists $hash{$array[1]});
    push @{$hash{$array[1]}}, $array[0];
}


#and now you do the Johnny Cash (walk the line)
my @line;
_Johnny(5);  # entry that you wish to query
foreach (@line){
  print $_ . ",";
}
#------------------------------------------------#
sub _Johnny {

my $x = shift;
push (@line,$x);
for (@{$hash{$x}}){
  _Johnny($_);
}
}
#------------------------------------------------#


__DATA__
3,1
5,1
4,3
2,7
6,4
8,2
7,6
11,5
12,5
43,11
15,11