sub plays_in_round { my ($p1, $p2, $n) = @_; $n++ if $n % 2; return undef if $p1 == $p2; ($p1, $p2) = ($p2, $p1) if $p1 > $p2; $p2 = $p1 if $p2 == $n; my $r = $p1 + $p2 - 2; $r %= $n - 1; $r || ($n - 1); }