run-length-encoder

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Danil Negrienko 2024-06-29 02:14:21 -04:00
parent 8d8a30b39c
commit dad68cb89f
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{
"authors": [
"Teapane"
],
"contributors": [
"angelikatyborska",
"CoderDennis",
"Cohen-Carlisle",
"dalexj",
"daveyarwood",
"devonestes",
"lex57ukr",
"lpil",
"neenjaw",
"parkerl",
"sotojuan",
"waiting-for-dev"
],
"files": {
"solution": [
"lib/run_length_encoder.ex"
],
"test": [
"test/run_length_encoder_test.exs"
],
"example": [
".meta/example.ex"
]
},
"blurb": "Implement run-length encoding and decoding.",
"source": "Wikipedia",
"source_url": "https://en.wikipedia.org/wiki/Run-length_encoding"
}

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

24
elixir/run-length-encoding/.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").
run_length_encoding-*.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/run_length_encoder.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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# Run-Length Encoding
Welcome to Run-Length Encoding on Exercism's Elixir Track.
If you need help running the tests or submitting your code, check out `HELP.md`.
## Instructions
Implement run-length encoding and decoding.
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.
For example we can represent the original 53 characters with only 13.
```text
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB" -> "12WB12W3B24WB"
```
RLE allows the original data to be perfectly reconstructed from the compressed data, which makes it a lossless data compression.
```text
"AABCCCDEEEE" -> "2AB3CD4E" -> "AABCCCDEEEE"
```
For simplicity, you can assume that the unencoded string will only contain the letters A through Z (either lower or upper case) and whitespace.
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.
## Source
### Created by
- @Teapane
### Contributed to by
- @angelikatyborska
- @CoderDennis
- @Cohen-Carlisle
- @dalexj
- @daveyarwood
- @devonestes
- @lex57ukr
- @lpil
- @neenjaw
- @parkerl
- @sotojuan
- @waiting-for-dev
### Based on
Wikipedia - https://en.wikipedia.org/wiki/Run-length_encoding

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defmodule RunLengthEncoder do
@digits ~w(0 1 2 3 4 5 6 7 8 9)
defguardp is_digit(char) when char in @digits
defp encode_reducer(char, []), do: [{char, 1}]
defp encode_reducer(char, [{char, count} | rest]), do: [{char, count + 1} | rest]
defp encode_reducer(char, rest), do: [{char, 1} | rest]
defp encode_mapper({char, 1}), do: char
defp encode_mapper({char, count}), do: "#{count}#{char}"
defp decode_reducer(digit, []) when is_digit(digit), do: [{nil, digit}]
defp decode_reducer(digit, [{nil, count} | rest]) when is_digit(digit), do: [{nil, count <> digit} | rest]
defp decode_reducer(char, [{nil, count} | rest]) when not is_digit(char), do: [{char, String.to_integer(count)} | rest]
defp decode_reducer(digit, rest) when is_digit(digit), do: [{nil, digit} | rest]
defp decode_reducer(char, rest), do: [{char, 1} | rest]
defp decode_mapper({char, 1}), do: char
defp decode_mapper({char, count}), do: String.duplicate(char, count)
@doc """
Generates a string where consecutive elements are represented as a data value and count.
"AABBBCCCC" => "2A3B4C"
For this example, assume all input are strings, that are all uppercase letters.
It should also be able to reconstruct the data into its original form.
"2A3B4C" => "AABBBCCCC"
"""
@spec encode(String.t()) :: String.t()
def encode(string) do
string
|> String.graphemes()
|> Enum.reduce([], &encode_reducer/2)
|> Enum.reverse()
|> Enum.map_join(&encode_mapper/1)
end
@spec decode(String.t()) :: String.t()
def decode(string) do
string
|> String.graphemes()
|> Enum.reduce([], &decode_reducer/2)
|> Enum.reverse()
|> Enum.map_join(&decode_mapper/1)
end
end

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defmodule RunLengthEncoder.MixProject do
use Mix.Project
def project do
[
app: :run_length_encoder,
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 RunLengthEncoderTest do
use ExUnit.Case
test "encode empty string" do
assert RunLengthEncoder.encode("") === ""
end
test "encode single characters only are encoded without count" do
assert RunLengthEncoder.encode("XYZ") === "XYZ"
end
test "encode string with no single characters" do
assert RunLengthEncoder.encode("AABBBCCCC") == "2A3B4C"
end
test "encode single characters mixed with repeated characters" do
assert RunLengthEncoder.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB") ===
"12WB12W3B24WB"
end
test "encode multiple whitespace mixed in string" do
assert RunLengthEncoder.encode(" hsqq qww ") === "2 hs2q q2w2 "
end
test "encode lowercase characters" do
assert RunLengthEncoder.encode("aabbbcccc") === "2a3b4c"
end
test "decode empty string" do
assert RunLengthEncoder.decode("") === ""
end
test "decode single characters only" do
assert RunLengthEncoder.decode("XYZ") === "XYZ"
end
test "decode string with no single characters" do
assert RunLengthEncoder.decode("2A3B4C") == "AABBBCCCC"
end
test "decode single characters with repeated characters" do
assert RunLengthEncoder.decode("12WB12W3B24WB") ===
"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
end
test "decode multiple whitespace mixed in string" do
assert RunLengthEncoder.decode("2 hs2q q2w2 ") === " hsqq qww "
end
test "decode lower case string" do
assert RunLengthEncoder.decode("2a3b4c") === "aabbbcccc"
end
test "encode followed by decode gives original string" do
original = "zzz ZZ zZ"
encoded = RunLengthEncoder.encode(original)
assert RunLengthEncoder.decode(encoded) === original
end
end

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