Fibonacci Sequence

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"},
  {:benchee, "~> 1.1"}
])

Navigation

Return Home Report An Issue

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.

Fibonacci Sequence

The Fibonacci Sequence is a series of the following numbers.

flowchart LR
a[0] --> b[1] --> c[1] --> d[2] --> e[3] --> f[5] --> g[8] --> h[13] --> i[21] --> k[34] --> ...

It’s created by taking the sum of the previous to numbers to get the next number.

So $fib(n) = fib(n-1) + fib(n - 2)$

You’ll notice that this is a recursive function. You’re going to create a Fibonacci module that can generate the $nth$ fibonacci number.

Example Solution

defmodule Fibonacci do
  def of(0), do: 0
  def of(1), do: 1

  def of(n) do
    of(n - 1) + of(n - 2)
  end
end

Implement the Fibonacci module as documented.

defmodule Fibonacci do
  @moduledoc """
  Documentation for the `Fibonacci` module.
  """

  @doc """
  Generate the nth fibonacci number.

  ## Examples

    iex> Fibonacci.of(0)
    0

    iex> Fibonacci.of(1)
    1

    iex> Fibonacci.of(2)
    1

    iex> Fibonacci.of(3)
    2

    iex> Fibonacci.of(4)
    3

    iex> Fibonacci.of(5)
    5

    iex> Fibonacci.of(6)
    8

    iex> Fibonacci.of(20)
    6765
  """
  def of(n) do
  end
end

Mark As Completed

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

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "fibonacci_reading"
    "exercises" -> "fibonacci_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 fibonacci-exercise
$ git add .
$ git commit -m "finish fibonacci exercise"
$ git push origin fibonacci-exercise

Create a pull request from your fibonacci-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.

If you are interested in joining the next academy cohort, sign up here to receive more news when it is available.

Up Next