perfect-numbers

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

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+{
+  "authors": [
+    "DoggettCK"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "devonestes",
+    "neenjaw",
+    "sotojuan"
+  ],
+  "files": {
+    "solution": [
+      "lib/perfect_numbers.ex"
+    ],
+    "test": [
+      "test/perfect_numbers_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.",
+  "source": "Taken from Chapter 2 of Functional Thinking by Neal Ford.",
+  "source_url": "https://www.oreilly.com/library/view/functional-thinking/9781449365509/"
+}

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

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+{"track":"elixir","exercise":"perfect-numbers","id":"a3a905652d3c4b7fbe13a8ea5819052b","url":"https://exercism.org/tracks/elixir/exercises/perfect-numbers","handle":"negrienko","is_requester":true,"auto_approve":false}

elixir/perfect-numbers/.formatter.exs

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

elixir/perfect-numbers/.gitignore

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+# 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").
+perfect_numbers-*.tar
+

elixir/perfect-numbers/HELP.md

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+# 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/perfect_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/perfect-numbers/README.md

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+# Perfect Numbers
+
+Welcome to Perfect Numbers on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.
+
+The Greek mathematician [Nicomachus][nicomachus] devised a classification scheme for positive integers, identifying each as belonging uniquely to the categories of [perfect](#perfect), [abundant](#abundant), or [deficient](#deficient) based on their [aliquot sum][aliquot-sum].
+The _aliquot sum_ is defined as the sum of the factors of a number not including the number itself.
+For example, the aliquot sum of `15` is `1 + 3 + 5 = 9`.
+
+## Perfect
+
+A number is perfect when it equals its aliquot sum.
+For example:
+
+- `6` is a perfect number because `1 + 2 + 3 = 6`
+- `28` is a perfect number because `1 + 2 + 4 + 7 + 14 = 28`
+
+## Abundant
+
+A number is abundant when it is less than its aliquot sum.
+For example:
+
+- `12` is an abundant number because `1 + 2 + 3 + 4 + 6 = 16`
+- `24` is an abundant number because `1 + 2 + 3 + 4 + 6 + 8 + 12 = 36`
+
+## Deficient
+
+A number is deficient when it is greater than its aliquot sum.
+For example:
+
+- `8` is a deficient number because `1 + 2 + 4 = 7`
+- Prime numbers are deficient
+
+## Task
+
+Implement a way to determine whether a given number is [perfect](#perfect).
+Depending on your language track, you may also need to implement a way to determine whether a given number is [abundant](#abundant) or [deficient](#deficient).
+
+[nicomachus]: https://en.wikipedia.org/wiki/Nicomachus
+[aliquot-sum]: https://en.wikipedia.org/wiki/Aliquot_sum
+
+## Source
+
+### Created by
+
+- @DoggettCK
+
+### Contributed to by
+
+- @angelikatyborska
+- @Cohen-Carlisle
+- @devonestes
+- @neenjaw
+- @sotojuan
+
+### Based on
+
+Taken from Chapter 2 of Functional Thinking by Neal Ford. - https://www.oreilly.com/library/view/functional-thinking/9781449365509/

elixir/perfect-numbers/lib/perfect_numbers.ex

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+defmodule PerfectNumbers do
+  @doc """
+  Determine the aliquot sum of the given `number`, by summing all the factors
+  of `number`, aside from `number` itself.
+
+  Based on this sum, classify the number as:
+
+  :perfect if the aliquot sum is equal to `number`
+  :abundant if the aliquot sum is greater than `number`
+  :deficient if the aliquot sum is less than `number`
+  """
+  @spec classify(number :: integer) :: {:ok, atom} | {:error, String.t()}
+  def classify(number) when number <= 0, do: {:error, "Classification is only possible for natural numbers."}
+  def classify(1), do: {:ok, :deficient}
+  def classify(number) do
+    sum =
+      number
+      |> divisors()
+      |> Enum.sum()
+
+    cond do
+      sum == number ->
+        {:ok, :perfect}
+
+      sum > number ->
+        {:ok, :abundant}
+
+      sum < number ->
+        {:ok, :deficient}
+    end
+  end
+
+  defp divisors(number) do
+    for i <- 1..round(number ** 0.5), reduce: [] do
+      acc -> if rem(number, i) == 0, do: [i, div(number, i) | acc], else: acc
+    end
+    |> Enum.uniq()
+    |> Enum.sort()
+    |> Enum.drop(-1)
+  end
+end

elixir/perfect-numbers/mix.exs

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+defmodule PerfectNumbers.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :perfect_numbers,
+      version: "0.1.0",
+      # elixir: "~> 1.8",
+      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/perfect-numbers/test/perfect_numbers_test.exs

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+defmodule PerfectNumbersTest do
+  use ExUnit.Case
+
+  describe "Perfect numbers" do
+    test "Smallest perfect number is classified correctly" do
+      assert PerfectNumbers.classify(6) == {:ok, :perfect}
+    end
+
+    test "Medium perfect number is classified correctly" do
+      assert PerfectNumbers.classify(28) == {:ok, :perfect}
+    end
+
+    test "Large perfect number is classified correctly" do
+      assert PerfectNumbers.classify(33_550_336) == {:ok, :perfect}
+    end
+  end
+
+  describe "Abundant numbers" do
+    test "Smallest abundant number is classified correctly" do
+      assert PerfectNumbers.classify(12) == {:ok, :abundant}
+    end
+
+    test "Medium abundant number is classified correctly" do
+      assert PerfectNumbers.classify(30) == {:ok, :abundant}
+    end
+
+    test "Large abundant number is classified correctly" do
+      assert PerfectNumbers.classify(33_550_335) == {:ok, :abundant}
+    end
+  end
+
+  describe "Deficient numbers" do
+    test "Smallest prime deficient number is classified correctly" do
+      assert PerfectNumbers.classify(2) == {:ok, :deficient}
+    end
+
+    test "Smallest non-prime deficient number is classified correctly" do
+      assert PerfectNumbers.classify(4) == {:ok, :deficient}
+    end
+
+    test "Medium deficient number is classified correctly" do
+      assert PerfectNumbers.classify(32) == {:ok, :deficient}
+    end
+
+    test "Large deficient number is classified correctly" do
+      assert PerfectNumbers.classify(33_550_337) == {:ok, :deficient}
+    end
+
+    test "Edge case (no factors other than itself) is classified correctly" do
+      assert PerfectNumbers.classify(1) == {:ok, :deficient}
+    end
+  end
+
+  describe "Invalid inputs" do
+    test "Zero is rejected (not a natural number)" do
+      assert PerfectNumbers.classify(0) ==
+               {:error, "Classification is only possible for natural numbers."}
+    end
+
+    test "Negative integer is rejected (not a natural number)" do
+      assert PerfectNumbers.classify(-1) ==
+               {:error, "Classification is only possible for natural numbers."}
+    end
+  end
+end

elixir/perfect-numbers/test/test_helper.exs

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