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# angelikatyborska's solution

## to Bowling in the Elixir Track

Published at Apr 29 2019 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Score a bowling game.

Bowling is a game where players roll a heavy ball to knock down pins arranged in a triangle. Write code to keep track of the score of a game of bowling.

## Scoring Bowling

The game consists of 10 frames. A frame is composed of one or two ball throws with 10 pins standing at frame initialization. There are three cases for the tabulation of a frame.

• An open frame is where a score of less than 10 is recorded for the frame. In this case the score for the frame is the number of pins knocked down.

• A spare is where all ten pins are knocked down by the second throw. The total value of a spare is 10 plus the number of pins knocked down in their next throw.

• A strike is where all ten pins are knocked down by the first throw. The total value of a strike is 10 plus the number of pins knocked down in the next two throws. If a strike is immediately followed by a second strike, then the value of the first strike cannot be determined until the ball is thrown one more time.

Here is a three frame example:

Frame 1 Frame 2 Frame 3
X (strike) 5/ (spare) 9 0 (open frame)

Frame 1 is (10 + 5 + 5) = 20

Frame 2 is (5 + 5 + 9) = 19

Frame 3 is (9 + 0) = 9

This means the current running total is 48.

The tenth frame in the game is a special case. If someone throws a strike or a spare then they get a fill ball. Fill balls exist to calculate the total of the 10th frame. Scoring a strike or spare on the fill ball does not give the player more fill balls. The total value of the 10th frame is the total number of pins knocked down.

For a tenth frame of X1/ (strike and a spare), the total value is 20.

For a tenth frame of XXX (three strikes), the total value is 30.

## Requirements

Write code to keep track of the score of a game of bowling. It should support two operations:

• `roll(pins : int)` is called each time the player rolls a ball. The argument is the number of pins knocked down.
• `score() : int` is called only at the very end of the game. It returns the total score for that game.

## Running tests

Execute the tests with:

``````\$ elixir bowling_test.exs
``````

### Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.

For example:

``````# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
``````

Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the test suite.

``````# ExUnit.configure exclude: :pending, trace: true
``````

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

## Source

The Bowling Game Kata at but UncleBob http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### bowling_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule BowlingTest do
use ExUnit.Case

defp roll_reduce(game, rolls) do
Enum.reduce(rolls, game, fn roll, game -> Bowling.roll(game, roll) end)
end

test "should be able to score a game with all zeros" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 0
end

@tag :pending
test "should be able to score a game with no strikes or spares" do
game = Bowling.start()
rolls = [3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 90
end

@tag :pending
test "a spare followed by zeros is worth ten points" do
game = Bowling.start()
rolls = [6, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 10
end

@tag :pending
test "points scored in the roll after a spare are counted twice" do
game = Bowling.start()
rolls = [6, 4, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 16
end

@tag :pending
test "consecutive spares each get a one roll bonus" do
game = Bowling.start()
rolls = [5, 5, 3, 7, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 31
end

@tag :pending
test "a spare in the last frame gets a one roll bonus that is counted once" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 3, 7]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 17
end

@tag :pending
test "a strike earns ten points in a frame with a single roll" do
game = Bowling.start()
rolls = [10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 10
end

@tag :pending
test "points scored in the two rolls after a strike are counted twice as a bonus" do
game = Bowling.start()
rolls = [10, 5, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 26
end

@tag :pending
test "consecutive strikes each get the two roll bonus" do
game = Bowling.start()
rolls = [10, 10, 10, 5, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 81
end

@tag :pending
test "a strike in the last frame gets a two roll bonus that is counted once" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 7, 1]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 18
end

@tag :pending
test "rolling a spare with the two roll bonus does not get a bonus roll" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 7, 3]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 20
end

@tag :pending
test "strikes with the two roll bonus do not get bonus rolls" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 10, 10]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 30
end

@tag :pending
test "a strike with the one roll bonus after a spare in the last frame does not get a bonus" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 3, 10]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 20
end

@tag :pending
test "all strikes is a perfect game" do
game = Bowling.start()
rolls = [10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 300
end

@tag :pending
test "rolls cannot score negative points" do
game = Bowling.start()
assert Bowling.roll(game, -1) == {:error, "Negative roll is invalid"}
end

@tag :pending
test "a roll cannot score more than 10 points" do
game = Bowling.start()
assert Bowling.roll(game, 11) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "two rolls in a frame cannot score more than 10 points" do
game = Bowling.start()
game = Bowling.roll(game, 5)
assert Bowling.roll(game, 6) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "bonus roll after a strike in the last frame cannot score more than 10 points" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10]
game = roll_reduce(game, rolls)
assert Bowling.roll(game, 11) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "two bonus rolls after a strike in the last frame cannot score more than 10 points" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 5]
game = roll_reduce(game, rolls)
assert Bowling.roll(game, 6) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "two bonus rolls after a strike in the last frame can score more than 10 points if one is a strike" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 10, 6]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == 26
end

@tag :pending
test "the second bonus rolls after a strike in the last frame cannot be a strike if the first one is not a strike" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 6]
game = roll_reduce(game, rolls)
assert Bowling.roll(game, 10) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "second bonus roll after a strike in the last frame cannot score more than 10 points" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 10]
game = roll_reduce(game, rolls)
assert Bowling.roll(game, 11) == {:error, "Pin count exceeds pins on the lane"}
end

@tag :pending
test "an unstarted game cannot be scored" do
game = Bowling.start()
assert Bowling.score(game) == {:error, "Score cannot be taken until the end of the game"}
end

@tag :pending
test "an incomplete game cannot be scored" do
game = Bowling.start()
rolls = [0, 0]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == {:error, "Score cannot be taken until the end of the game"}
end

@tag :pending
test "cannot roll if game already has ten frames" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
game = roll_reduce(game, rolls)
assert Bowling.roll(game, 0) == {:error, "Cannot roll after game is over"}
end

@tag :pending
test "bonus rolls for a strike in the last frame must be rolled before score can be calculated" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == {:error, "Score cannot be taken until the end of the game"}
end

@tag :pending
test "both bonus rolls for a strike in the last frame must be rolled before score can be calculated" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 10]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == {:error, "Score cannot be taken until the end of the game"}
end

@tag :pending
test "bonus roll for a spare in the last frame must be rolled before score can be calculated" do
game = Bowling.start()
rolls = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 3]
game = roll_reduce(game, rolls)
assert Bowling.score(game) == {:error, "Score cannot be taken until the end of the game"}
end
end``````
``````defmodule Bowling do
alias __MODULE__, as: Game

@type throw :: nil | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10

defmodule Frame do
defstruct throw1: nil, throw2: nil

@type t :: %__MODULE__{throw1: Bowling.throw(), throw2: Bowling.throw()}
end

defstruct frames: [], fill_balls: []

@type t :: %__MODULE__{frames: list(Frame.t()), fill_balls: list(throw())}

@max_pins 10
@frames_in_game 10
@game_not_over_error {:error, "Score cannot be taken until the end of the game"}
@game_over_error {:error, "Cannot roll after game is over"}
@negative_error {:error, "Negative roll is invalid"}
@too_much_error {:error, "Pin count exceeds pins on the lane"}

@doc """
Creates a new game of bowling that can be used to store the results of
the game
"""

@spec start() :: any
def start do
%Game{}
end

@doc """
Records the number of pins knocked down on a single roll. Returns `any`
unless there is something wrong with the given number of pins, in which
case it returns a helpful message.
"""

@spec roll(any, integer) :: any | String.t()
def roll(game, roll) do
with {:can_roll, true} <- {:can_roll, can_roll?(game)},
{:validate_roll, :ok} <- {:validate_roll, validate_roll(game, roll)} do
cond do
game.frames == [] ->

should_do_second_throw?(hd(game.frames)) ->

should_do_fill_ball?(game) ->

true ->
end
else
{:can_roll, false} -> @game_over_error
{:validate_roll, error} -> error
end
end

@doc """
Returns the score of a given game of bowling if the game is complete.
If the game isn't complete, it returns a helpful message.
"""

@spec score(any) :: integer | String.t()
def score(game) do
if can_roll?(game) do
@game_not_over_error
else
do_score(Enum.reverse(game.frames), 0, game.fill_balls)
end
end

defp do_score([], score, _), do: score

defp do_score([frame | next_frames], score, fill_balls) do
cond do
strike?(frame) -> @max_pins + sum_two_next_throws(next_frames, fill_balls)
spare?(frame) -> @max_pins + sum_next_throw(next_frames, fill_balls)
true -> frame.throw1 + frame.throw2
end

end

defp can_roll?(%Game{frames: frames}) when length(frames) < @frames_in_game, do: true

defp can_roll?(%Game{frames: frames} = game) when length(frames) == @frames_in_game do
should_do_second_throw?(hd(frames)) || should_do_fill_ball?(game)
end

defp strike?(%Frame{throw1: @max_pins}), do: true
defp strike?(%Frame{}), do: false

defp spare?(%Frame{throw1: @max_pins}), do: false
defp spare?(%Frame{throw1: nil}), do: false
defp spare?(%Frame{throw2: nil}), do: false
defp spare?(%Frame{throw1: t1, throw2: t2}), do: t1 + t2 == @max_pins

defp should_do_second_throw?(%Frame{throw1: @max_pins}), do: false
defp should_do_second_throw?(%Frame{throw1: t, throw2: nil}), do: !is_nil(t)
defp should_do_second_throw?(%Frame{}), do: false

defp should_do_fill_ball?(%Game{frames: frames, fill_balls: fill_balls}) do
if length(frames) == @frames_in_game do
[h | _] = frames

(strike?(h) && length(fill_balls) < 2) ||
(spare?(h) && length(fill_balls) < 1)
else
false
end
end

defp sum_next_throw([next_frame | _], _fill_balls) do
next_frame.throw1
end

defp sum_next_throw([], [fill_ball | _]) do
fill_ball
end

defp sum_two_next_throws([next_frame | t], fill_balls) do
if strike?(next_frame) do
@max_pins + if t == [], do: hd(fill_balls), else: hd(t).throw1
else
next_frame.throw1 + next_frame.throw2
end
end

defp sum_two_next_throws([], [fill_ball1, fill_ball2]) do
fill_ball1 + fill_ball2
end

%{game | frames: [%Frame{throw1: roll} | game.frames]}
end

[frame | t] = game.frames
%{game | frames: [%Frame{frame | throw2: roll} | t]}
end

%{game | fill_balls: [roll | game.fill_balls]}
end

defp validate_roll(_game, roll) when roll < 0, do: @negative_error
defp validate_roll(_game, roll) when roll > @max_pins, do: @too_much_error

defp validate_roll(game, roll) do
with [frame | _] <- game.frames do
cond do
should_do_second_throw?(frame) && frame.throw1 + roll > @max_pins ->
@too_much_error

should_do_fill_ball?(game) && game.fill_balls != [@max_pins] &&
Enum.sum([roll | game.fill_balls]) > @max_pins ->
@too_much_error

true ->
:ok
end
else
_ -> :ok
end
end
end``````