Hi.
In response to Pm's "Scripting games in Perl6" I've decided to implement some of them in Perl6.
Let's start with easiest "2008: Beginners Event 1"
Task is to calculate number of different pairs of cards.
sub fact($n) {
$n <= 1 ?? 1 !! $n*fact($n-1);
}
sub calculate_pairs(@pairs) {
my %h;
# Calculate number of distinct cards.
++%h{$_} for @pairs;
# Sum of C^N_2
[+] map { int(fact($^a) / 2) }, %h.values;
};
Trivial mathematical solution: number of different pairs for given amount of cards is C^n_2. So, I group cards, calculate number of combinations in different group and sum them.
Little trick: if number of cards in group equals to 1 than int(...) will return 0.
Update: masak++ for pointing to use.perl.org strange reaction on <=
0 0 1 3 12 60 360
C^n_2 is of course n!/(n-2)!2!, or n(n-1)/2:
0 0 1 3 6 10 15
It’s just [*] 1. It’s not even worth putting into a sub.
