my %neighbours;
for (my $i = 0; $i < @domain1; $i++) {
    push @{$neighbours{$domain[$i]}}, $neighbours{$domain[$i-1]} if $i > 0;
    push @{$neighbours{$domain[$i]}}, $neighbours{$domain[$i+1]} if $i < $#domain1;
}
my @neighbours = map {@$_} @neighbours{map {/(.*)/; $1} <INPUTDOMAINLIST>};