Exercism: 3x+1

erlang/collatz-conjecture/.exercism/config.json

@@ -0,0 +1,27 @@
+{
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture",
+  "authors": [
+    "NobbZ"
+  ],
+  "contributors": [
+    "ErikSchierboom",
+    "iHiD",
+    "JordanAdams",
+    "juhlig",
+    "kytrinyx",
+    "wojtii"
+  ],
+  "files": {
+    "solution": [
+      "src/collatz_conjecture.erl"
+    ],
+    "test": [
+      "test/collatz_conjecture_tests.erl"
+    ],
+    "example": [
+      ".meta/example.erl"
+    ]
+  },
+  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
+  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+}

erlang/collatz-conjecture/.exercism/metadata.json

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+{"track":"erlang","exercise":"collatz-conjecture","id":"6258a251cb6e4d80b70d021f2052b335","url":"https://exercism.org/tracks/erlang/exercises/collatz-conjecture","handle":"JBiason","is_requester":true,"auto_approve":false}

erlang/collatz-conjecture/HELP.md

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+# Help
+
+## Running the tests
+
+You can run the tests by running the following command from the exercise directory.
+
+```bash
+$ rebar3 eunit
+```
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/collatz_conjecture.erl` 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 [Erlang track's documentation](https://exercism.org/docs/tracks/erlang)
+- [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.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [Exercism related BEAM support channel on gitter](https://gitter.im/exercism/xerlang)
+- [Erlang Documentation](http://www.erlang.org/doc.html)
+- [Learn You Some Erlang for Great Good](http://learnyousomeerlang.com)
+- [StackOverflow](http://stackoverflow.com/)

erlang/collatz-conjecture/README.md

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+# Collatz Conjecture
+
+Welcome to Collatz Conjecture on Exercism's Erlang 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
+
+- @NobbZ
+
+### Contributed to by
+
+- @ErikSchierboom
+- @iHiD
+- @JordanAdams
+- @juhlig
+- @kytrinyx
+- @wojtii
+
+### Based on
+
+An unsolved problem in mathematics named after mathematician Lothar Collatz - https://en.wikipedia.org/wiki/3x_%2B_1_problem

erlang/collatz-conjecture/rebar.config

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+%% Erlang compiler options
+{erl_opts, [debug_info, warnings_as_errors]}.
+
+{deps, [{erl_exercism, "0.1.2"}]}.
+
+{dialyzer, [
+  {warnings, [underspecs, no_return]},
+  {get_warnings, true},
+  {plt_apps, top_level_deps}, % top_level_deps | all_deps
+  {plt_extra_apps, []},
+  {plt_location, local}, % local | "/my/file/name"
+  {plt_prefix, "rebar3"},
+  {base_plt_apps, [stdlib, kernel, crypto]},
+  {base_plt_location, global}, % global | "/my/file/name"
+  {base_plt_prefix, "rebar3"}
+]}.
+
+%% eunit:test(Tests)
+{eunit_tests, []}.
+%% Options for eunit:test(Tests, Opts)
+{eunit_opts, [verbose]}.
+
+%% == xref ==
+
+{xref_warnings, true}.
+
+%% xref checks to run
+{xref_checks, [undefined_function_calls, undefined_functions,
+  locals_not_used, exports_not_used,
+  deprecated_function_calls, deprecated_functions]}.

erlang/collatz-conjecture/src/collatz_conjecture.app.src

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+{application, collatz_conjecture,
+  [{description, "exercism.io - collatz-conjecture"},
+    {vsn, "0.0.1"},
+    {modules, []},
+    {registered, []},
+    {applications, [kernel,
+      stdlib]},
+    {env, []}
+  ]}.

erlang/collatz-conjecture/src/collatz_conjecture.erl

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+-module(collatz_conjecture).
+
+-export([steps/1]).
+
+
+steps(1) -> 0;
+steps(N) when N =< 0 -> error(badarg);
+steps(N) when (N rem 2 == 0) -> 1 + steps(N div 2);
+steps(N) -> 1 + steps(3*N+1).

erlang/collatz-conjecture/test/collatz_conjecture_tests.erl

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+%% Generated with 'testgen v0.2.0'
+%% Revision 2 of the exercises generator was used
+%% https://github.com/exercism/problem-specifications/raw/42dd0cea20498fd544b152c4e2c0a419bb7e266a/exercises/collatz-conjecture/canonical-data.json
+%% This file is automatically generated from the exercises canonical data.
+
+-module(collatz_conjecture_tests).
+
+-include_lib("erl_exercism/include/exercism.hrl").
+-include_lib("eunit/include/eunit.hrl").
+
+
+
+
+'1_zero_steps_for_one_test_'() ->
+    {"zero steps for one",
+     ?_assertMatch(0, collatz_conjecture:steps(1))}.
+
+'2_divide_if_even_test_'() ->
+    {"divide if even",
+     ?_assertMatch(4, collatz_conjecture:steps(16))}.
+
+'3_even_and_odd_steps_test_'() ->
+    {"even and odd steps",
+     ?_assertMatch(9, collatz_conjecture:steps(12))}.
+
+'4_large_number_of_even_and_odd_steps_test_'() ->
+    {"large number of even and odd steps",
+     ?_assertMatch(152, collatz_conjecture:steps(1000000))}.
+
+'5_zero_is_an_error_test_'() ->
+    {"zero is an error",
+     ?_assertError(badarg, collatz_conjecture:steps(0))}.
+
+'6_negative_value_is_an_error_test_'() ->
+    {"negative value is an error",
+     ?_assertError(badarg, collatz_conjecture:steps(-15))}.

tracks.txt

@@ -3,7 +3,7 @@ C			I
 C#			I
 Clojure			I
 Elixir			I
-Erlang
+Erlang			I
 Haskell
 Kotlin
 Lua