my $counterexamples = join "\n", map( pin(), 1 .. 10000 ), '';

my $digits = "\0" x 10;
substr $digits, $_, 1, $_ for $counterexamples =~ /\d/g;
( $digits ^= '0123456789' ) =~ tr/\0//d;

$counterexamples =~ s/^\d{4}\n//gm;