collatz

collatz-conjecture/.exercism/config.json

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+{
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
+  "authors": [
+    "Tuxified"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "devonestes",
+    "neenjaw",
+    "sotojuan"
+  ],
+  "files": {
+    "solution": [
+      "lib/collatz_conjecture.ex"
+    ],
+    "test": [
+      "test/collatz_conjecture_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
+  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+}

collatz-conjecture/.exercism/metadata.json

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+{"track":"elixir","exercise":"collatz-conjecture","id":"3fe9485ac17a4145b1f00dd25b0832e3","url":"https://exercism.org/tracks/elixir/exercises/collatz-conjecture","handle":"rjNemo","is_requester":true,"auto_approve":false}

collatz-conjecture/.formatter.exs

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

collatz-conjecture/.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").
+collatz_conjecture-*.tar
+

collatz-conjecture/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/collatz_conjecture.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)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- 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.
+If you can't find what you're looking for in the documentation, feel free to ask help in the Exercism's BEAM [gitter channel](https://gitter.im/exercism/xerlang).

collatz-conjecture/README.md

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+# Collatz Conjecture
+
+Welcome to Collatz Conjecture on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n. If n is even, divide n by 2 to get n / 2. If n is
+odd, multiply n by 3 and add 1 to get 3n + 1. Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will
+always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps. So for input n = 12, the return value would be 9.
+
+## Source
+
+### Created by
+
+- @Tuxified
+
+### Contributed to by
+
+- @angelikatyborska
+- @Cohen-Carlisle
+- @devonestes
+- @neenjaw
+- @sotojuan
+
+### Based on
+
+An unsolved problem in mathematics named after mathematician Lothar Collatz - https://en.wikipedia.org/wiki/3x_%2B_1_problem

collatz-conjecture/lib/collatz_conjecture.ex

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+defmodule CollatzConjecture do
+  @moduledoc """
+  The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+  Take any positive integer `n`. If `n` is even, divide `n` by `2` to get `n/2`. If `n` is odd, multiply `n` by `3` and add `1` to get `3n+1`.
+
+  Repeat the process indefinitely. The conjecture states that no matter which number you start with, you will always reach `1` eventually.
+  """
+
+  @doc """
+  calc/1 takes an integer and returns the number of steps required to get the
+  number to 1 when following the rules:
+    - if number is odd, multiply with 3 and add 1
+    - if number is even, divide by 2
+  """
+  @spec calc(input :: pos_integer()) :: non_neg_integer()
+  def calc(1), do: 0
+  def calc(input) when input > 0, do: compute(input, 0)
+
+  defp compute(1, steps), do: steps
+  defp compute(current, steps) when rem(current, 2) == 0, do: compute(div(current, 2), steps + 1)
+  defp compute(current, steps) when rem(current, 2) != 0, do: compute(3 * current + 1, steps + 1)
+end

collatz-conjecture/mix.exs

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+defmodule CollatzConjecture.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :collatz_conjecture,
+      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

collatz-conjecture/test/collatz_conjecture_test.exs

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+defmodule CollatzConjectureTest do
+  use ExUnit.Case
+
+  test "zero steps for one" do
+    assert CollatzConjecture.calc(1) == 0
+  end
+
+  test "zero is an error" do
+    assert_raise FunctionClauseError, fn -> CollatzConjecture.calc(0) end
+  end
+
+  test "divide if even" do
+    assert CollatzConjecture.calc(16) == 4
+  end
+
+  test "even and odd steps" do
+    assert CollatzConjecture.calc(12) == 9
+  end
+
+  test "Large number of even and odd steps" do
+    assert CollatzConjecture.calc(1_000_000) == 152
+  end
+
+  test "start with odd step" do
+    assert CollatzConjecture.calc(21) == 7
+  end
+
+  test "more steps than starting number" do
+    assert CollatzConjecture.calc(7) == 16
+  end
+
+  test "negative value is an error " do
+    assert_raise FunctionClauseError, fn -> CollatzConjecture.calc(-15) end
+  end
+
+  test "string as input value is an error " do
+    assert_raise FunctionClauseError, fn -> CollatzConjecture.calc("fubar") end
+  end
+end

collatz-conjecture/test/test_helper.exs

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

high-score/test/high_score_test.exs

@@ -175,12 +175,7 @@ defmodule HighScoreTest do
         |> HighScore.get_players()
         |> Enum.sort()
 
-      assert players == [
-               "Chris McCord",
-               "Dave Thomas",
-               "José Valim",
-               "Saša Jurić"
-             ]
+      assert players == ["Chris McCord", "Dave Thomas", "José Valim", "Saša Jurić"]
     end
   end
 end