Question

I’m working through the Ruby Koans, and I’m having a bit of trouble figuring out what is going wrong with a method I’ve written. I’m in about_scoring_project.rb, and I’ve written the score method for the dice game:

def score(dice)
  return 0 if dice == []
  sum = 0
  rolls = dice.inject(Hash.new(0)) { |result, element| result[element] += 1; result; }
  rolls.each { |key, value| 
    # special condition for rolls of 1
    if key == 1  
      sum += 1000 | value -= 3 if value >= 3
      sum += 100*value
      next
    end
    sum += 100*key | value -= 3 if value >= 3
    sum += 50*value if key == 5 && value > 0
  }
  return sum
end

For those unfamiliar with the exercise:

Greed is a dice game where you roll up to five dice to accumulate
points. The following “score” function will be used to 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.

I run into trouble when I try to run the last test in the file: assert_equal 550, score([5,5,5,5])

For some reason I am returning 551 instead of 550. Thanks for your help!

Answer 1

This is because you’re really adding the result of a | operator (Bitwise OR) to the total score:

sum += 100*key | value -= 3 if value >= 3 # This is 501 in your case

Proof:

irb(main):004:0> value = 4
=> 4
irb(main):005:0> 100 * 5 | value -= 3 # This should be read as (500) | 1 which is 501
=> 501

So rewrite it like this:

if value >= 3
  sum += 100 * key
  value -= 3
end