use Data::Dumper;

my @sets =
    ([ 0, 1, 2, 3,          7, 8, 9, 10, 11, 12, 13, 14, 15,     ],
     [ 0,       3,          7, 8,    10, 11,     13, 14,     16, ],
     [ 0, 1, 2, 3,    5,    7, 8,    10, 11, 12, 13, 14,     16, ],
     [       2, 3, 4,    6, 7, 8,    10, 11, 12,     14,     16, ],
     [ 0, 1, 2, 3,          7, 8, 9, 10, 11,     13, 14, 15,     ]);

my @common = ();

### helpers
sub max_element {
    my $max = -1;
    for (@sets) {
        $max = $_->[0] if $_->[0] > $max;
    }
    return $max;
}

sub all_the_same {
    my $element;
    for (@sets) {
        if (not defined $element) {
            $element = $_->[0];
        } else {
            return 0 if $element != $_->[0];
        }
    }
    return 1;
}

### main loop
my $done = 0;
while (not $done) {

    foreach (@sets) {
        $done++ if @$_ == 0;
    }

    if (all_the_same()) {
        push @common, $sets[0][0];
        shift @$_ for @sets;
    } else {
        my $max = max_element();
        for (@sets) {
            shift @$_ if $_->[0] < $max;
        }
    }


    ## uncomment these to see how it works step by step:
    # print Dumper(\@sets, \@common), "\n";
    # <STDIN>

}

print "@common\n";