Problem

Having coded in Java and C# for quite some years, I’m currently learning Ruby. I’m working my way through the Ruby Koans tutorial. At some point, you are to implement a method that calculates the game-score of a dice-game called Greed.

I came up with this recursive Java/C#-like method. It passes all the supplied unit tests, so technically it’s correct.

Now I’m wondering: Is this good Ruby code? If not, how would a “Rubyist” write this method? And possibly: Why? I’m also not so happy about the amount of duplicate code but can’t think

of a better Rubyish way.

```
def score(dice) #dice is an array of numbers, i.e. [3,4,5,3,3]
return 0 if(dice == [] || dice == nil)
dice.sort!
return 1000 + score(dice[3..-1]) if(dice[0..2] == [1,1,1])
return 600 + score(dice[3..-1]) if(dice[0..2] == [6,6,6])
return 500 + score(dice[3..-1]) if(dice[0..2] == [5,5,5])
return 400 + score(dice[3..-1]) if(dice[0..2] == [4,4,4])
return 300 + score(dice[3..-1]) if(dice[0..2] == [3,3,3])
return 200 + score(dice[3..-1]) if(dice[0..2] == [2,2,2])
return 100 + score(dice[1..-1]) if(dice[0] == 1)
return 50 + score(dice[1..-1]) if(dice[0] == 5)
return 0 + score(dice[1..-1]);
end
```

**Some background (if needed)**

```
# Greed is a dice game where you roll up to five dice to accumulate
# points. 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 fours is 400 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:
class AboutScoringProject < EdgeCase::Koan
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_a_single_roll_of_1_is_100
assert_equal 200, score([1,1])
end
def test_score_of_multiple_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_mixed_is_sum
assert_equal 250, score([2,5,2,2,3])
assert_equal 550, score([5,5,5,5])
end
def test_score_of_a_triple_1_is_1000A
assert_equal 1150, score([1,1,1,5,1])
end
def test_score_of_a_triple_1_is_1000B
assert_equal 350, score([3,4,5,3,3])
end
def test_score_of_a_triple_1_is_1000C
assert_equal 250, score([1,5,1,2,4])
end
end
```

Solution

There are a few issues with the code:

- Do not check for
`== nil`

when it is not specified as a valid value for the method. Here,checking for it and returning 0 might mask another problem. - Do not use return statements unless necessary. In ruby, almost everything is an expression, and methods return the value of the last expression. Here you can use
`if...elsif`

, or`case`

instead of a series of`if`

statement. - Do not modify parameters that come into your function (
`dice.sort!`

). - Do not use recursion if it makes the code less readable.

Here is a version of the code with the advice above applied:

```
def score(dice)
score = 0
counts = dice.each_with_object(Hash.new(0)) { |x, h| h[x] += 1 }
(1..6).each do |i|
if counts[i] >= 3
score += (i == 1 ? 1000 : 100 * i)
counts[i] = [counts[i] - 3, 0].max
end
score += counts[i] * (i == 1 ? 100 : 50)
end
score
end
```

@glebm has some very good points. I want to also introduce a different style. Here is how I would approach this problem.

```
def score dice
dice.group_by(&:to_i).inject(0) do |score, combo|
score + combos_score(*combo) + ones_score(*combo) + fives_score(*combo)
end
end
def combos_score dice_value, dice_with_value
number_of_bonues = [dice_with_value.size - 2, 0].max
bonus_for(dice_value) * number_of_bonues
end
def bonus_for dice_value
dice_value == 1 ? 1000 : dice_value * 100
end
def ones_score dice_value, dice_with_value
return 0 if dice_value != 1 || dice_with_value.size > 2
dice_with_value.size * 100
end
def fives_score dice_value, dice_with_value
return 0 if dice_value != 5 || dice_with_value.size > 2
dice_with_value.size * 50
end
```

I like that

- Logic for each scoring scenario is isolated together
- There isn’t a need to build a special Hash that would calculate the score.
- Use of the built in Enumerable#group_by to grab similar die together
- Small methods that are easy to test