use strict;
use warnings;

my %items = (
    a => [ qw/one six/ ],
    b => [ qw/two three five/ ],
    c => [ qw/one two five/ ],
    d => [ qw/one seven five/ ],
    e => [ qw/one two five/ ],
    f => [ qw/one two four seven/ ],
    g => [ qw/one two five/ ],
    h => [ qw/one two three five/ ],
);
my $tuple = 2;

# Build a reverse HoH
my %rHoH;
while (my ($k,$v) = each %items) {
    $rHoH{$_}{$k} = undef for @$v;
}

# Determine all possible n-tuples
my @accum = ();
for my $elem (keys %rHoH) {
    push @accum, ([$elem], map { @$_ < $tuple ? [@$_, $elem] : () } @a
+ccum);
}
@accum = grep { @$_ == $tuple } @accum;

# For each tuple in @accum, mark which items contained each member
# then count how many got marked for all of them
my @count;
for my $a (0..$#accum) {
    my %ic; # item counter
    for my $n (@{$accum[$a]}) {
        ++$ic{$_} for keys %{$rHoH{$n}};
    }
    $count[$a] = grep {$ic{$_} == $tuple} keys %ic;
}

# print the tuples out, with their counts, highest to lowest
printf "[%s]: $count[$_]\n", join(',', @{$accum[$_]})
  for sort {$count[$b] <=> $count[$a]}
      grep { $count[$_] > 1 }
      0..$#accum;
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