Solution to Greed Ruby Koan

gistfile1.rb

class Array
  def occurrences_of(match)
    if match.respond_to? :map
      return match.map { |item| self.occurrences_of(item) } 
    else
      return self.select{ |number| match == number }.size
    end
  end
end

def score rolls
  result = 0

  rules = [:single_double_rule, :triple_quadruple_quintuple_sextuple_rule, :three_pairs_rule, :straight_rule]  
  rules.each do |rule|    
    rule_result, is_final_result = method(rule).call rolls
    return rule_result if is_final_result

    result += rule_result
  end

  return result  
end

def single_double_rule rolls
  { 1 => 100, 5 => 50 }.reduce(0) do |result, (dice_roll_result, points)| 
    result += points * rolls.occurrences_of(dice_roll_result).modulo(6).modulo(5).modulo(4).modulo(3)
  end
end

def triple_quadruple_quintuple_sextuple_rule rolls
  hat_trick_points  =  { 1 => 1000, 2 => 200, 3 => 300, 4 => 400, 5 => 500, 6 => 600 }
  hat_trick_points.reduce(0) do |result, (dice_roll_result, points)| 
    occurrences = rolls.occurrences_of(dice_roll_result)
    result = result +
             points * occurrences.div(3) +
             points * occurrences.div(4) +
             points * occurrences.div(5) * 2 +
             points * occurrences.div(6) * 3           
  end  
end

def three_pairs_rule rolls  
  return 800, true if rolls.occurrences_of(1..6).select { |occurrence|  occurrence == 2 }.length == 3
  return 0
end

def straight_rule rolls
  return 1200, true if rolls.occurrences_of(1..6).select { |occurrence|  occurrence == 1 }.length == 6
  return 0
end