sub n_choose_k { my ($n, $k) = @_; # f($n) = $n! return f($n)/f($k)/f($n-$k); } #### sub n_choose_k { my ($n, $k) = @_; my $t = 1; for my $i (1 .. $k) { $t *= $n - $k + $i; $t /= $i; } return $t; }