Rate regex  hash    gf
regex 1.94/s    --  -73%  -78%
hash  7.17/s  269%    --  -17%
gf    8.67/s  347%   21%    --

##</code><code>##

use strict;
use warnings;

use Time::HiRes;
use Benchmark ':all';

my @data = (1000..9999);

cmpthese (-2, {
   hash  => 'hash()',
   gf  => 'gf()',
   regex => 'regex()',
});

sub regex {  
   my @keep;
   foreach my $line (@data) {
      chomp $line;
      for ( split //, $line ) {
         my @a = ($line =~ m/$_/g);
         if (@a == 2) { push @keep, $line; last; }
      }
   }
}

sub hash {
   my @keep;     # numbers to keep
   foreach my $line (@data) {
       chomp $line;
       my %count;
       ++$count{$_} for split '', $line;
       push @keep, $line if grep { $_ == 2 } values %count
   }
}

sub gf {
  my @keep = grep {my %d; map {$d{$_}++} split ''; grep {$_ == 2} values %d} @data;
}