bob@domain sue@domain ... foo@domain bar@other_domain #### #!/usr/bin/perl use strict; my $frame = 10; my @fifo = (); my @seen = ('') x $frame; while (my $email = ) { chomp $email; next if $email =~ m/^\s*$/; my $domain = get_domain($email); if (seen($domain, \@seen)) { push @fifo, [$domain, $email]; } else { # try to pull next problem email off fifo buffer if (@fifo and not seen($fifo[0]->[0], \@seen)){ cout($fifo[0]->[1]); shift @seen; push @seen, $fifo[0]->[0]; my $fifo = shift @fifo; # make sure current email is not same domain # that we just pulled off fifo.... if ( $fifo->[0] eq $domain ) { push @fifo, [$domain, $email]; next; } } cout($email); shift @seen; push @seen, $domain; } } # we have failed if our fifo is not empty, solution decrease frame width if (@fifo) { cout($_->[1]) for @fifo; die sprintf("Still had fifo buffer of length %d with frame width %d\n", scalar @fifo, $frame); } sub cout {print "$_[0]\n" } sub get_domain { my ($email) = @_; (my $domain) = $email =~ m/\@([\w\-\.]+)/; die "Can't find domain for $email at line $.\n" unless $domain; return $domain; } sub seen { my ($domain, $seen) = @_; for (@$seen) { return 1 if $_ eq $domain; } return 0; } __DATA__ b@b.com b@b.com b@b.com b@b.com b@b.com b@b.com b@b.com b@b.com b@b.com b@b.com a@aa.com a@ab.com a@ac.com a@ad.com a@ae.com a@af.com a@ag.com a@ah.com a@ai.com a@aj.com a@ak.com a@al.com a@am.com a@an.com a@ao.com a@ap.com a@aq.com a@ar.com a@as.com a@at.com a@au.com a@av.com a@aw.com a@ax.com a@ay.com a@az.com a@ba.com a@bb.com a@bc.com a@bd.com a@be.com a@bf.com a@bg.com a@bh.com a@bi.com a@bj.com a@bk.com a@bl.com a@bm.com a@bn.com a@bo.com a@bp.com a@bq.com a@br.com a@bs.com a@bt.com a@bu.com a@bv.com a@bw.com a@bx.com a@by.com a@bz.com