Card Counting

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Setup

Ensure you type the ea keyboard shortcut to evaluate all Elixir cells before starting. Alternatively you can evaluate the Elixir cells as you read.

Card Counting

We’re going to build some logic for a card counting application. Card counting is a strategy used in card games to determine if there are more high cards or low cards in the deck.

There are 13 numbered cards in a common deck of playing cards.

We’ll use integers 1 to 13 to represent playing cards. Cards are either low, normal, or high.

flowchart LR
subgraph low cards
  direction LR
  1 --- 2 --- 3 --- 4 --- 5 --- 6
end

subgraph Normal Cards
  direction LR
  7 --- 8 --- 9
end

subgraph High Cards
  direction LR
  10 --- 11 --- 12 --- 13
end

In order to track if there are more high cards left in the deck, or low cards left in the deck, you’ll track a running count starting at 0.

• When dealt a low card decrease the count by 1.
• When dealt a high card increase the count by 1.
• When dealt a normal card do nothing.

Bind Card Counts

Bind integers low, normal, and high to track the amount to increase or decrease the current count by. You will use these variables in further exercises.

Example solution

low = -1
normal = 0
high = 1

Enter your solution below.

High Card

The initial count is 0. You have been dealt one high card. Use arithmetic operators and the bound variables above to determine the new count.

Example solution

initial_count = 0
initial_count + high

Enter your solution below.

Low Card

The initial count is 0. You have been dealt one low card. Use arithmetic operators and the bound variables above to determine the new count.

Example solution

initial_count = 0
initial_count + low

Enter your solution below.

Multiple Cards

The initial count is 5. You have been dealt five high cards, two low cards, and two normal cards. Use arithmetic operators and the bound variables above to determine the new count.

Example solution

initial_count = 5
initial_count + high * 5 + low * 2 + normal * 2

You could omit the normal cards or allow high and low cards to balance each other, however if the increment/decrement value changes then your code would break.

Enter your solution below.

Bonus: Determining Card Values

You are dealt three cards of a random value between 1 and 13. You can use Enum.random/1 to generate a random number.

random_card = Enum.random(1..13)

Generate three random cards, use the values of the three randomly generated cards to determine the current count given the initial count is 0.

Example solution

random_card1 = Enum.random(1..13)
random_card2 = Enum.random(1..13)
random_card3 = Enum.random(1..13)

cards =
  Enum.map([random_card1, random_card2, random_card3], fn random_card ->
    cond do
      random_card <= 6 -> low
      random_card >= 10 -> high
      true -> normal
    end
  end)

Enum.sum(cards)

You could omit the normal cards or allow high and low cards to balance each other, however if the increment/decrement value changes then your code would break.

Enter your solution below.

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "card_counting_reading"
    "exercises" -> "card_counting_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b card-counting-exercise
$ git add .
$ git commit -m "finish card counting exercise"
$ git push origin card-counting-exercise

Create a pull request from your card-counting-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

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