#!/usr/bin/env perl

use strict;
use warnings;

my %data = (
    A => [qw{ant bee cat dog eel fly gnu hog}],
    B => [qw{ant cat eel gnu}],
    C => [qw{bee dog fly hog}],
    D => [qw{cat fly ant}],
    E => [qw{ant dog gnu}],
    F => [qw{gnu bee}],
    G => [qw{eel hog}],
    H => [qw{zoo}],
    I => [qw{}],
);
my (%venn, %temp);

for my $set (sort keys %data) {
    my @elems = @{$data{$set}};
    @elems = ('') unless @elems;

    for my $elem (@elems) {
        push @{$temp{$elem}}, $set;
    }
}

for my $elem (keys %temp) {
    my @sets = @{$temp{$elem}};

    for my $i (0 .. $#sets) {
        my @subsets = @sets[$i .. $#sets];
        my $key = shift @subsets;
        push @{$venn{$key}}, $elem;

        for my $set (@subsets) {
            $key .= "-$set";
            push @{$venn{$key}}, $elem;
        }
    }
}

my $fmt = "%-7s  %s  %s\n";
{
    no warnings 'qw';
    printf $fmt, qw{Sets # Elements};
    printf $fmt, qw{---- - --------};
}

for my $sets (sort keys %venn) {
    printf $fmt, $sets, 0+@{$venn{$sets}},
        join ' ', sort @{$venn{$sets}};
}