>>264 Perl

@md = ([5, 15], [5, 16], [5, 19],
[6, 17], [6, 18],
[7, 14], [7, 16],
[8, 14], [8, 15], [8, 17]);
push @{$c{$$_[1]}}, $$_[0] for @md;
push @{$d{$$_[0]}}, $$_[1] for grep{1 < @{$c{$$_[1]}}} @md;
while (($m, $v) = each %d) {
print "$m/$$v[0]\n" if 1== @$v;
}

実行結果

$ perl 9_264.pl
6/17