my %card;
++$card{$_} for @hand;
$score += $_ * ($_ - 1) for values %card;
# 1 * 0 = 0  (0  points for 1 of a kind)
# 2 * 1 = 2  (2  points for 2 of a kind)
# 3 * 2 = 6  (6  points for 3 of a kind)
# 4 * 3 = 12 (12 points for 4 of a kind)