Use strings instead of arrays and hashes: 
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;

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In reply to Re^5: Testing Random Code by jwkrahn
in thread Testing Random Code by Ovid

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