greed_koan.rb

def score dice
  {1 => 100, 2 => 0, 3 => 0, 4 => 0, 5 => 50, 6 => 0}.map do |(n, score)|
    occurences = dice.count n
    (occurences / 3) * (n == 1 ? 1000 : n * 100) + (occurences % 3) * score
  end.reduce :+
end