lucas-numbers

elixir/lucas-numbers/.exercism/config.json

@@ -0,0 +1,21 @@
+{
+  "authors": [
+    "neenjaw"
+  ],
+  "contributors": [
+    "angelikatyborska"
+  ],
+  "files": {
+    "solution": [
+      "lib/lucas_numbers.ex"
+    ],
+    "test": [
+      "test/lucas_numbers_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "language_versions": ">=1.10",
+  "blurb": "Learn about streams by generating the Lucas number sequence."
+}

elixir/lucas-numbers/.exercism/metadata.json

@@ -0,0 +1 @@
+{"track":"elixir","exercise":"lucas-numbers","id":"b7780e9479024bcb9aedfcad6acca6e5","url":"https://exercism.org/tracks/elixir/exercises/lucas-numbers","handle":"negrienko","is_requester":true,"auto_approve":false}

elixir/lucas-numbers/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

elixir/lucas-numbers/.gitignore

@@ -0,0 +1,27 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+lucas_numbers-*.tar
+
+
+# Temporary files for e.g. tests
+/tmp

elixir/lucas-numbers/HELP.md

@@ -0,0 +1,75 @@
+# Help
+
+## Running the tests
+
+From the terminal, change to the base directory of the exercise then execute the tests with:
+
+```bash
+$ mix test
+```
+
+This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
+
+Documentation:
+
+* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
+* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
+
+## Pending tests
+
+In test suites of practice exercises, all but the first test have been tagged to be 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:
+
+```elixir
+# @tag :pending
+test "shouting" do
+  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
+end
+```
+
+If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
+
+```bash
+$ mix test --include pending
+```
+
+Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
+
+```elixir
+# ExUnit.configure(exclude: :pending, trace: true)
+```
+
+## Useful `mix test` options
+
+* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
+* `--failed` - runs only tests that failed the last time they ran
+* `--max-failures` - the suite stops evaluating tests when this number of test failures
+is reached
+* `--seed 0` - disables randomization so the tests in a single file will always be ran
+in the same order they were defined in
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/lucas_numbers.ex` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
+- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.

elixir/lucas-numbers/HINTS.md

@@ -0,0 +1,29 @@
+# Hints
+
+## General
+
+- Use the built-in [(linked) list type][list].
+- Use the built-in [`Stream`][stream] module functions to create a stream
+
+## 1. Generate the base cases
+
+- You can use multiple [function clauses][multiple-fn-clauses] and [pattern-matching][pattern-matching] to create the base case functions.
+
+## 2. Create the generalized case
+
+- Use the [`Stream.iterate/2`][stream-iterate] function to generate a sequence of numbers, with the next being created from the previous.
+- The starting numbers are `2` then `1`, which you can pass in together using a tuple to make a pair `{2, 1}`
+- Make sure the next number is the sum of the two numbers previous to it.
+- To evaluate the stream to a list, use an [`Enum`][enum] function.
+
+## 3. Catch bad arguments
+
+- Use a [guard][guards] to catch the cases when an integer isn't passed as an argument to `generate/1`.
+
+[enum]: https://hexdocs.pm/elixir/Enum.html#content
+[guards]: https://hexdocs.pm/elixir/patterns-and-guards.html#guards
+[list]: https://hexdocs.pm/elixir/lists-and-tuples.html#linked-lists
+[multiple-fn-clauses]: https://hexdocs.pm/elixir/modules-and-functions.html#function-definition
+[pattern-matching]: https://hexdocs.pm/elixir/pattern-matching.html#pattern-matching
+[stream]: https://hexdocs.pm/elixir/Stream.html#content
+[stream-iterate]: https://hexdocs.pm/elixir/Stream.html#iterate/2

elixir/lucas-numbers/README.md

@@ -0,0 +1,67 @@
+# Lucas Numbers
+
+Welcome to Lucas Numbers on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
+
+## Introduction
+
+## Streams
+
+All functions in the [`Enum` module][exercism-enum] are _eager_. When performing multiple operations on enumerables with the `Enum` module, each operation is going to generate an intermediate result.
+
+The `Stream` module is a _lazy_ alternative to the _eager_ `Enum` module. It offers many of the same functions as `Enum`, but instead of generating intermediate results, it builds a series of computations that are only executed once the stream is passed to a function from the `Enum` module.
+
+Streams implement the _Enumerable [protocol][exercism-protocols]_ and are composable -- you can chain them together to create more complex functionality.
+
+[exercism-enum]: https://exercism.org/tracks/elixir/concepts/enum
+[exercism-protocols]: https://exercism.org/tracks/elixir/concepts/protocols
+
+## Instructions
+
+You are a huge fan of the [Numberphile Youtube channel](https://www.youtube.com/watch?v=PeUbRXnbmms) and you just saw a cool video about the _Lucas Number Sequence_. You want to create this sequence using Elixir.
+
+While designing your function, you want to make use of _lazy evaluation_, so that you can generate as many numbers as you want, but only if you need to -- So you decide to use a stream:
+
+## 1. Generate the base cases
+
+You know that the sequence has two starting numbers which don't follow the same rule. Write two base case clauses to return these numbers:
+
+```elixir
+LucasNumbers.generate(1)
+# => [2]
+
+LucasNumbers.generate(2)
+# => [2, 1]
+```
+
+## 2. Create the generalized case
+
+For any sequence longer than 2, you know that you need to add the previous two numbers to get the next number and so on. Write the generalized case.
+
+```elixir
+LucasNumbers.generate(3)
+# => [2, 1, 3]
+
+LucasNumbers.generate(4)
+# => [2, 1, 3, 4]
+```
+
+## 3. Catch bad arguments
+
+Later, you find someone is using your function and having problems because they are using incorrect arguments. Add a guard clause to raise an error if a non-integer or an integer less than 1 is used to generate the sequence:
+
+```elixir
+LucasNumbers.generate("Hello World")
+# => ** (ArgumentError) count must be specified as an integer >= 1
+```
+
+## Source
+
+### Created by
+
+- @neenjaw
+
+### Contributed to by
+
+- @angelikatyborska

elixir/lucas-numbers/lib/lucas_numbers.ex

@@ -0,0 +1,17 @@
+defmodule LucasNumbers do
+  @moduledoc """
+  Lucas numbers are an infinite sequence of numbers which build progressively
+  which hold a strong correlation to the golden ratio (φ or ϕ)
+
+  E.g.: 2, 1, 3, 4, 7, 11, 18, 29, ...
+  """
+
+  def generate(count) when is_integer(count) and count > 0 do
+    {2, 1}
+    |> Stream.iterate(fn {a, b} -> {b, a + b} end)
+    |> Stream.map(&elem(&1, 0))
+    |> Enum.take(count)
+  end
+
+  def generate(_count), do: raise(ArgumentError, "count must be specified as an integer >= 1")
+end

elixir/lucas-numbers/mix.exs

@@ -0,0 +1,28 @@
+defmodule LucasNumbers.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :lucas_numbers,
+      version: "0.1.0",
+      # elixir: "~> 1.10",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

elixir/lucas-numbers/test/lucas_numbers_test.exs

@@ -0,0 +1,112 @@
+defmodule LucasNumbersTest do
+  use ExUnit.Case
+
+  @tag task_id: 1
+  test "generates a sequence of length 1" do
+    assert LucasNumbers.generate(1) == [2]
+  end
+
+  @tag task_id: 1
+  test "generates a sequence of length 2" do
+    assert LucasNumbers.generate(2) == [2, 1]
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 3" do
+    assert LucasNumbers.generate(3) == [2, 1, 3]
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 4" do
+    assert LucasNumbers.generate(4) == [2, 1, 3, 4]
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 5" do
+    sequence = [2, 1, 3, 4, 7]
+
+    assert LucasNumbers.generate(5) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 6" do
+    sequence = [2, 1, 3, 4, 7, 11]
+
+    assert LucasNumbers.generate(6) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 7" do
+    sequence = [2, 1, 3, 4, 7, 11, 18]
+
+    assert LucasNumbers.generate(7) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 8" do
+    sequence = [2, 1, 3, 4, 7, 11, 18, 29]
+
+    assert LucasNumbers.generate(8) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 9" do
+    sequence = [2, 1, 3, 4, 7, 11, 18, 29, 47]
+
+    assert LucasNumbers.generate(9) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 10" do
+    sequence = [2, 1, 3, 4, 7, 11, 18, 29, 47, 76]
+
+    assert LucasNumbers.generate(10) == sequence
+  end
+
+  @tag task_id: 2
+  test "generates a sequence of length 25" do
+    sequence = [
+      2,
+      1,
+      3,
+      4,
+      7,
+      11,
+      18,
+      29,
+      47,
+      76,
+      123,
+      199,
+      322,
+      521,
+      843,
+      1364,
+      2207,
+      3571,
+      5778,
+      9349,
+      15127,
+      24476,
+      39603,
+      64079,
+      103_682
+    ]
+
+    assert LucasNumbers.generate(25) == sequence
+  end
+
+  @tag task_id: 3
+  test "catch incorrect non-integer arguments" do
+    assert_raise ArgumentError, "count must be specified as an integer >= 1", fn ->
+      LucasNumbers.generate("Hello world!")
+    end
+  end
+
+  @tag task_id: 3
+  test "catch incorrect integer arguments" do
+    assert_raise ArgumentError, "count must be specified as an integer >= 1", fn ->
+      LucasNumbers.generate(-1)
+    end
+  end
+end

elixir/lucas-numbers/test/test_helper.exs

@@ -0,0 +1,2 @@
+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true, seed: 0)