#!/usr/bin/perl
use warnings;
use strict;

{
   my @round_aoh;
   my @players = qw/John Jane Bill Suzi Bret Erin Eric Teri/;
   my $rounds = @players - 1;

   for my $round ( 1..$rounds ) {
      for my $player ( @players ) {
         next if $round_aoh[$round]{$player};
         $round_aoh[$round]{$player} = 'pending';
         my ($opponent) = grep {unmatched( $player, $_, \@round_aoh)}
                          grep {not $round_aoh[$round]{$_}} @players;
         $round_aoh[$round]{$player  } = $opponent;
         $round_aoh[$round]{$opponent} = $player;
      }
   }

   # Now, show what we did.
   for my $round ( 1..$rounds ) {
      print "Round $round\n";
      for my $player ( keys %{$round_aoh[$round]} ) {
         # crude hack to skip dupes: A vs B  :  B vs A
         next unless $player gt $round_aoh[$round]{$player};
         print "   $player vs $round_aoh[$round]{$player}\n";
      }
   }
}

sub unmatched {
   my ($player, $opponent, $round_arefoh) = @_;
   for my $round ( 1..@$round_arefoh) {
      if (defined $round_arefoh->[$round]{$player}
              and $round_arefoh->[$round]{$player} eq $opponent) {
         return 0;
      }
   }
   return 1;
}