use strict;
use warnings;

# Create 100 x 100 datastructure:

my @uc = ( 'AA' .. 'DV' );
my @lc = ( 'aa' .. 'dv' );

my %index;
for my $k ( @uc ) {
  for my $v ( @lc ) {
    $index{$k}{$v} = 1;
  }
}

# Parse it:

my $score;
for my $k ( @uc ) {    # or: for my $k ( @subset_1 )
  for my $v ( @lc ) {  # or: for my $v ( @subset_2 )
    $score += $index{$k}{$v} || 0;
  }
}

print $score;