сollatz-сonjecture

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Danil Negrienko 2024-06-26 23:06:52 -04:00
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{
"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"
]
},
"blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
"source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
"source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
}

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{"track":"elixir","exercise":"collatz-conjecture","id":"ccd0e87e9b8944838d567e25ffb84d23","url":"https://exercism.org/tracks/elixir/exercises/collatz-conjecture","handle":"negrienko","is_requester":true,"auto_approve":false}

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

24
elixir/collatz-conjecture/.gitignore vendored Normal file
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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

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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)
- 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.

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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

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defmodule CollatzConjecture do
@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(input) when is_integer(input) and input > 0, do: collatz(input)
defp collatz(input, steps \\ 0)
defp collatz(1, steps), do: steps
defp collatz(input, steps) when rem(input, 2) == 0, do: collatz(div(input, 2), steps + 1)
defp collatz(input, steps), do: collatz(input * 3 + 1, steps + 1)
end

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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

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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

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