@D1 = map lc $_, $D1 =~ /(\w+)/g ;
my @D2 = map lc $_, $D2 =~ /(\w+)/g ;

my %D2 = () ;

@D2{@D2} = (1) x scalar @D2 ;

my $total = scalar @D1 + scalar @D1 ;

my $intersection = 0 ;

# count the number of words in common
foreach my $word ( @D1 ) {
    ++$intersection if $D2{$word} ;
}

my $similarity = 2 * ( $intersection/$total ) ;

print "\n$similarity\n\n" ;