about_scoring_project.rb

require 'edgecase'


# Greed is a dice game where you roll up to five dice to accumulate
# points.  The following "score" function will be used calculate the
# score of a single roll of the dice.
#
# A greed roll is scored as follows:
#
# * A set of three ones is 1000 points
#   
# * A set of three numbers (other than ones) is worth 100 times the
#   number. (e.g. three fives is 500 points).
#
# * A one (that is not part of a set of three) is worth 100 points.
#
# * A five (that is not part of a set of three) is worth 50 points.
#
# * Everything else is worth 0 points.
#
#
# Examples:
#
# score([1,1,1,5,1]) => 1150 points
# score([2,3,4,6,2]) => 0 points
# score([3,4,5,3,3]) => 350 points
# score([1,5,1,2,4]) => 250 points
#
# More scoring examples are given in the tests below:
#
# Your goal is to write the score method.

class AboutScoringAssignment < EdgeCase::Koan

  def score(dice)
    total_score = 0    
    [2,3,4,6].each do |number| 
      total_score += score_for_number(dice, number, number * 100, 0)
    end
    
    total_score += score_for_number(dice, 5, 500, 50)
    total_score += score_for_number(dice, 1, 1000, 100)
  end
  
  def score_for_number(dice, selection, value_of_triple, value_of_single)    
    selected = dice.select{|item| item == selection}
    three_or_more = selected.size >= 3
    remaining = three_or_more ? selected[3, selected.size] : selected
    remaining.inject(three_or_more ? value_of_triple : 0){|total, item| total + value_of_single}    
  end

  def test_score_of_an_empty_list_is_zero
    assert_equal 0, score([])
  end

  def test_score_of_a_single_roll_of_5_is_50
    assert_equal 50, score([5])
  end

  def test_score_of_a_single_roll_of_1_is_100
    assert_equal 100, score([1])
  end

  def test_score_of_mulitple_1s_and_5s_is_the_sum_of_individual_scores
    assert_equal 300, score([1,5,5,1])
  end

  def test_score_of_single_2s_3s_4s_and_6s_are_zero
    assert_equal 0, score([2,3,4,6])
  end

  def test_score_of_a_triple_1_is_1000
    assert_equal 1000, score([1,1,1])
  end

  def test_score_of_other_triples_is_100x
    assert_equal 200, score([2,2,2])
    assert_equal 300, score([3,3,3])
    assert_equal 400, score([4,4,4])
    assert_equal 500, score([5,5,5])
    assert_equal 600, score([6,6,6])
  end

  def test_score_of_more_than_triple_others_is_still_100x
    assert_equal 200, score([2,2,2,2])
    assert_equal 300, score([3,3,3,3,3])
    assert_equal 400, score([4,4,4,4])
    assert_equal 600, score([6,6,6,6])
  end

  def test_score_of_mixed_is_sum
    assert_equal 250, score([2,5,2,2,3])
    assert_equal 550, score([5,5,5,5])
    assert_equal 1100, score([1,1,1,1])
  end
end

@youngnh

Not sure I agree on the readable, but I do like your reduction-based algorithm idea.

@zeedunk

Per our earlier face-2-face discussion a few thoughts:

• The work done to setup for each call to score_for_number is a bit cumbersome (some are done via 'each', others are singular stand outs, and the need/use of each parameter isn't immediately clear looking just at the score function). Looking at the code w/o first reading ALL of the instructions meant I didn't immediately follow why the distinction was being made. It would be great if the difference in scoring schemes could be separated and all values iterated over in the same way.
• The score_for_number method itself seems a bit muddy. You really only need the number of each type of die, not the actual die values to calculate a score. This would also get rid of the need for the last inject replaced by a simple expression (possibly with a call to an integer flooring function)
• Other than that, thanks for putting this up.

@youngnh - Thanks for the feedback. I think that would certainly be a simplification and I'll start hacking on that as soon as I get a chance.

@benjaminplee - I agree that the code doesn't clearly express why five and one are special cases. Integrating that with Nate's suggestion will be a fun challenge. As far the last inject, well, I keep reaching for inject because it's my new favorite toy. :) You're right though, it is unnecessary there.

Thanks again guys!