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use strict;
use warnings;
...
           - ($x * $y * $z);

my @only_two = $answer->elements();

{
   1 => [ 0, 1, 2 ],
...
  12 => [ 0, 1, 2 ],
  13 => [ 0, 1, 2 ],
}

use List::Compare;
sub elements_found_in_exactly_n_lists {
...
my @only_two = elements_found_in_exactly_n_lists(
  2, \@array1, \@array2, \@array3,
);