use warnings;
use strict;

my @data = qw(
    21112340    21112341    21112342    21112343
    21112344    21112345    21112346    21112347
    21112348    21112349    21112350    21112351
);

my %sixpack;

for my $item (@data) {
    my $suffix = chop($item);
    $sixpack{$item}{$suffix}++;
}

for my $six (sort keys %sixpack) {
    if (scalar(keys %{$sixpack{$six}}) == 10) {
        print "$six\n";
    }
    else {
        print "$six$_\n" for sort keys %{$sixpack{$six}};
    }
}