run-length-encoder
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{
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"authors": [
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"Teapane"
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],
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"contributors": [
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"angelikatyborska",
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"CoderDennis",
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"Cohen-Carlisle",
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"dalexj",
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"daveyarwood",
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"devonestes",
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"lex57ukr",
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"lpil",
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"neenjaw",
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"parkerl",
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"sotojuan",
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"waiting-for-dev"
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],
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"files": {
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"solution": [
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"lib/run_length_encoder.ex"
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],
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"test": [
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"test/run_length_encoder_test.exs"
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],
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"example": [
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".meta/example.ex"
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]
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},
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"blurb": "Implement run-length encoding and decoding.",
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"source": "Wikipedia",
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"source_url": "https://en.wikipedia.org/wiki/Run-length_encoding"
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}
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{"track":"elixir","exercise":"run-length-encoding","id":"df85d72f5fcc49efad7a6f2e236c7872","url":"https://exercism.org/tracks/elixir/exercises/run-length-encoding","handle":"negrienko","is_requester":true,"auto_approve":false}
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# Used by "mix format"
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[
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inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
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]
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# The directory Mix will write compiled artifacts to.
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/_build/
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# If you run "mix test --cover", coverage assets end up here.
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/cover/
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# The directory Mix downloads your dependencies sources to.
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/deps/
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# Where third-party dependencies like ExDoc output generated docs.
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/doc/
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# Ignore .fetch files in case you like to edit your project deps locally.
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/.fetch
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# If the VM crashes, it generates a dump, let's ignore it too.
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erl_crash.dump
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# Also ignore archive artifacts (built via "mix archive.build").
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*.ez
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# Ignore package tarball (built via "mix hex.build").
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run_length_encoding-*.tar
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# Help
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## Running the tests
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From the terminal, change to the base directory of the exercise then execute the tests with:
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```bash
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$ mix test
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```
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This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
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Documentation:
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* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
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* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
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## Pending tests
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In test suites of practice exercises, all but the first test have been tagged to be skipped.
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Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
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For example:
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```elixir
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# @tag :pending
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test "shouting" do
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assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
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end
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```
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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:
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```bash
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$ mix test --include pending
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```
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Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
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```elixir
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# ExUnit.configure(exclude: :pending, trace: true)
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```
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## Useful `mix test` options
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* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
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* `--failed` - runs only tests that failed the last time they ran
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* `--max-failures` - the suite stops evaluating tests when this number of test failures
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is reached
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* `--seed 0` - disables randomization so the tests in a single file will always be ran
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in the same order they were defined in
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## Submitting your solution
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You can submit your solution using the `exercism submit lib/run_length_encoder.ex` command.
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This command will upload your solution to the Exercism website and print the solution page's URL.
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It's possible to submit an incomplete solution which allows you to:
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- See how others have completed the exercise
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- Request help from a mentor
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## Need to get help?
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If you'd like help solving the exercise, check the following pages:
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- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
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- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
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- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
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- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
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Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
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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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# Run-Length Encoding
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Welcome to Run-Length Encoding on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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## Instructions
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Implement run-length encoding and decoding.
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Run-length encoding (RLE) is a simple form of data compression, where runs (consecutive data elements) are replaced by just one data value and count.
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For example we can represent the original 53 characters with only 13.
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```text
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"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB" -> "12WB12W3B24WB"
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```
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RLE allows the original data to be perfectly reconstructed from the compressed data, which makes it a lossless data compression.
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```text
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"AABCCCDEEEE" -> "2AB3CD4E" -> "AABCCCDEEEE"
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```
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For simplicity, you can assume that the unencoded string will only contain the letters A through Z (either lower or upper case) and whitespace.
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This way data to be encoded will never contain any numbers and numbers inside data to be decoded always represent the count for the following character.
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## Source
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### Created by
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- @Teapane
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### Contributed to by
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- @angelikatyborska
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- @CoderDennis
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- @Cohen-Carlisle
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- @dalexj
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- @daveyarwood
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- @devonestes
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- @lex57ukr
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- @lpil
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- @neenjaw
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- @parkerl
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- @sotojuan
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- @waiting-for-dev
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### Based on
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Wikipedia - https://en.wikipedia.org/wiki/Run-length_encoding
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defmodule RunLengthEncoder do
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@digits ~w(0 1 2 3 4 5 6 7 8 9)
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defguardp is_digit(char) when char in @digits
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defp encode_reducer(char, []), do: [{char, 1}]
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defp encode_reducer(char, [{char, count} | rest]), do: [{char, count + 1} | rest]
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defp encode_reducer(char, rest), do: [{char, 1} | rest]
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defp encode_mapper({char, 1}), do: char
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defp encode_mapper({char, count}), do: "#{count}#{char}"
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defp decode_reducer(digit, []) when is_digit(digit), do: [{nil, digit}]
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defp decode_reducer(digit, [{nil, count} | rest]) when is_digit(digit), do: [{nil, count <> digit} | rest]
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defp decode_reducer(char, [{nil, count} | rest]) when not is_digit(char), do: [{char, String.to_integer(count)} | rest]
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defp decode_reducer(digit, rest) when is_digit(digit), do: [{nil, digit} | rest]
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defp decode_reducer(char, rest), do: [{char, 1} | rest]
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defp decode_mapper({char, 1}), do: char
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defp decode_mapper({char, count}), do: String.duplicate(char, count)
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@doc """
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Generates a string where consecutive elements are represented as a data value and count.
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"AABBBCCCC" => "2A3B4C"
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For this example, assume all input are strings, that are all uppercase letters.
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It should also be able to reconstruct the data into its original form.
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"2A3B4C" => "AABBBCCCC"
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"""
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@spec encode(String.t()) :: String.t()
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def encode(string) do
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string
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|> String.graphemes()
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|> Enum.reduce([], &encode_reducer/2)
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|> Enum.reverse()
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|> Enum.map_join(&encode_mapper/1)
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end
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@spec decode(String.t()) :: String.t()
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def decode(string) do
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string
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|> String.graphemes()
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|> Enum.reduce([], &decode_reducer/2)
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|> Enum.reverse()
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|> Enum.map_join(&decode_mapper/1)
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end
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end
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defmodule RunLengthEncoder.MixProject do
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use Mix.Project
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def project do
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[
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app: :run_length_encoder,
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version: "0.1.0",
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# elixir: "~> 1.8",
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start_permanent: Mix.env() == :prod,
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deps: deps()
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]
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end
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# Run "mix help compile.app" to learn about applications.
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def application do
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[
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extra_applications: [:logger]
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]
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end
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# Run "mix help deps" to learn about dependencies.
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defp deps do
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[
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# {:dep_from_hexpm, "~> 0.3.0"},
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# {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
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]
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end
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end
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defmodule RunLengthEncoderTest do
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use ExUnit.Case
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test "encode empty string" do
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assert RunLengthEncoder.encode("") === ""
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end
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test "encode single characters only are encoded without count" do
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assert RunLengthEncoder.encode("XYZ") === "XYZ"
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end
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test "encode string with no single characters" do
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assert RunLengthEncoder.encode("AABBBCCCC") == "2A3B4C"
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end
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test "encode single characters mixed with repeated characters" do
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assert RunLengthEncoder.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB") ===
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"12WB12W3B24WB"
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end
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test "encode multiple whitespace mixed in string" do
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assert RunLengthEncoder.encode(" hsqq qww ") === "2 hs2q q2w2 "
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end
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test "encode lowercase characters" do
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assert RunLengthEncoder.encode("aabbbcccc") === "2a3b4c"
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end
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test "decode empty string" do
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assert RunLengthEncoder.decode("") === ""
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end
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test "decode single characters only" do
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assert RunLengthEncoder.decode("XYZ") === "XYZ"
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end
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test "decode string with no single characters" do
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assert RunLengthEncoder.decode("2A3B4C") == "AABBBCCCC"
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end
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test "decode single characters with repeated characters" do
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assert RunLengthEncoder.decode("12WB12W3B24WB") ===
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"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
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end
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test "decode multiple whitespace mixed in string" do
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assert RunLengthEncoder.decode("2 hs2q q2w2 ") === " hsqq qww "
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end
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test "decode lower case string" do
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assert RunLengthEncoder.decode("2a3b4c") === "aabbbcccc"
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end
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test "encode followed by decode gives original string" do
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original = "zzz ZZ zZ"
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encoded = RunLengthEncoder.encode(original)
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assert RunLengthEncoder.decode(encoded) === original
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end
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end
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ExUnit.start()
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ExUnit.configure(exclude: :pending, trace: true)
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