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[ Implementation ] Run-Length Encoding (#744)
💜²⁹ -- 🤝 https://forum.exercism.org/t/new-exercise-contributions/4077
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‎config.json

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"practices": [],
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"prerequisites": [],
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"difficulty": 1
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},
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{
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"slug": "run-length-encoding",
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"name": "Run-Length Encoding",
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"uuid": "8997f6f2-a8c3-42b5-94fc-12d0d386a64e",
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"practices": [],
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"prerequisites": [],
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"difficulty": 1
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}
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]
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},

‎exercises/practice/run-length-encoding/.docs/instructions.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.

‎exercises/practice/run-length-encoding/.meta/config.json

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{
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"authors": [
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"habere-et-dispertire"
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],
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"files": {
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"solution": [
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"lib/RunLengthEncoding.rakumod"
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],
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"test": [
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"t/run-length-encoding.rakutest"
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],
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"example": [
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".meta/solutions/lib/RunLengthEncoding.rakumod"
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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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}

‎exercises/practice/run-length-encoding/.meta/solutions/lib/RunLengthEncoding.rakumod

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unit module RunLengthEncoding;
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grammar RLE {
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token TOP { <pair>+ }
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token pair { <tally>? <element> }
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token tally { <digit>+ }
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token element { <alpha> | ' ' }
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}
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class RLE::Decode {
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method TOP ($/) { make $<pair>.map( *.made ).join }
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method pair ($/) { make $<element>.made x ( $<tally>.made // 1 ) }
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method tally ($/) { make $/.Int }
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method element ($/) { make $/.Str }
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}
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sub rle-decode ($compressed) is export {
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RLE.parse( $compressed, actions => RLE::Decode ).made
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}
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sub rle-encode ($raw) is export {
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given $raw.comb( / ( [<digit>+]? ) [<alpha> | ' ']+ % <same> / )
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.map( { .chars == 1 ?? $_ !! .chars ~ .comb.head } )
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.join
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-> $compressed {
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fail unless $raw eq rle-decode($compressed);
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return $compressed
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}
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}

‎exercises/practice/run-length-encoding/.meta/solutions/t/run-length-encoding.rakutest

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../../../t/run-length-encoding.rakutest

‎exercises/practice/run-length-encoding/.meta/template-data.yaml

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properties:
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encode:
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test: |-
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sprintf(q :to 'END', %case<input><string>.Str.raku, %case<expected>.Str.raku, %case<description>.raku);
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cmp-ok(
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rle-encode(%s),
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"eq",
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%s,
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%s,
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);
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END
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decode:
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test: |-
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sprintf(q :to 'END', %case<input><string>.Str.raku, %case<expected>.Str.raku, %case<description>.raku);
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cmp-ok(
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rle-decode(%s),
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"eq",
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%s,
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%s,
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);
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END
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consistency:
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test: |-
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sprintf(q :to 'END', %case<input><string>.Str.raku, %case<expected>.Str.raku, %case<description>.raku);
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cmp-ok(
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rle-decode(rle-encode(%s)),
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"eq",
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%s,
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%s,
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);
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END
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unit: module
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example: |-
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grammar RLE {
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token TOP { <pair>+ }
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token pair { <tally>? <element> }
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token tally { <digit>+ }
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token element { <alpha> | ' ' }
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}
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class RLE::Decode {
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method TOP ($/) { make $<pair>.map( *.made ).join }
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method pair ($/) { make $<element>.made x ( $<tally>.made // 1 ) }
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method tally ($/) { make $/.Int }
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method element ($/) { make $/.Str }
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}
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sub rle-decode ($compressed) is export {
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RLE.parse( $compressed, actions => RLE::Decode ).made
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}
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sub rle-encode ($raw) is export {
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given $raw.comb( / ( [<digit>+]? ) [<alpha> | ' ']+ % <same> / )
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.map( { .chars == 1 ?? $_ !! .chars ~ .comb.head } )
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.join
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-> $compressed {
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fail unless $raw eq rle-decode($compressed);
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return $compressed
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}
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}
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stub: |-
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sub rle-encode ($raw) is export {
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}
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sub rle-decode ($compressed) is export {
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}

‎exercises/practice/run-length-encoding/.meta/tests.toml

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[ad53b61b-6ffc-422f-81a6-61f7df92a231]
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description = "run-length encode a string -> empty string"
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[52012823-b7e6-4277-893c-5b96d42f82de]
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description = "run-length encode a string -> single characters only are encoded without count"
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[b7868492-7e3a-415f-8da3-d88f51f80409]
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description = "run-length encode a string -> string with no single characters"
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[859b822b-6e9f-44d6-9c46-6091ee6ae358]
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description = "run-length encode a string -> single characters mixed with repeated characters"
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[1b34de62-e152-47be-bc88-469746df63b3]
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description = "run-length encode a string -> multiple whitespace mixed in string"
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[abf176e2-3fbd-40ad-bb2f-2dd6d4df721a]
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description = "run-length encode a string -> lowercase characters"
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[7ec5c390-f03c-4acf-ac29-5f65861cdeb5]
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description = "run-length decode a string -> empty string"
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[ad23f455-1ac2-4b0e-87d0-b85b10696098]
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description = "run-length decode a string -> single characters only"
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[21e37583-5a20-4a0e-826c-3dee2c375f54]
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description = "run-length decode a string -> string with no single characters"
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[1389ad09-c3a8-4813-9324-99363fba429c]
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description = "run-length decode a string -> single characters with repeated characters"
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[3f8e3c51-6aca-4670-b86c-a213bf4706b0]
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description = "run-length decode a string -> multiple whitespace mixed in string"
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[29f721de-9aad-435f-ba37-7662df4fb551]
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description = "run-length decode a string -> lowercase string"
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[2a762efd-8695-4e04-b0d6-9736899fbc16]
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description = "encode and then decode -> encode followed by decode gives original string"

‎exercises/practice/run-length-encoding/lib/RunLengthEncoding.rakumod

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unit module RunLengthEncoding;
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sub rle-encode ($raw) is export {
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}
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sub rle-decode ($compressed) is export {
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}

‎exercises/practice/run-length-encoding/t/run-length-encoding.rakutest

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#!/usr/bin/env raku
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use Test;
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use lib $?FILE.IO.parent(2).add('lib');
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use RunLengthEncoding;
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cmp-ok( # begin: ad53b61b-6ffc-422f-81a6-61f7df92a231
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rle-encode(""),
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"eq",
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"",
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"run-length encode a string: empty string",
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); # end: ad53b61b-6ffc-422f-81a6-61f7df92a231
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cmp-ok( # begin: 52012823-b7e6-4277-893c-5b96d42f82de
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rle-encode("XYZ"),
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"eq",
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"XYZ",
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"run-length encode a string: single characters only are encoded without count",
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); # end: 52012823-b7e6-4277-893c-5b96d42f82de
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cmp-ok( # begin: b7868492-7e3a-415f-8da3-d88f51f80409
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rle-encode("AABBBCCCC"),
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"eq",
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"2A3B4C",
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"run-length encode a string: string with no single characters",
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); # end: b7868492-7e3a-415f-8da3-d88f51f80409
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cmp-ok( # begin: 859b822b-6e9f-44d6-9c46-6091ee6ae358
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rle-encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"),
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"eq",
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"12WB12W3B24WB",
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"run-length encode a string: single characters mixed with repeated characters",
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); # end: 859b822b-6e9f-44d6-9c46-6091ee6ae358
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cmp-ok( # begin: 1b34de62-e152-47be-bc88-469746df63b3
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rle-encode(" hsqq qww "),
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"eq",
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"2 hs2q q2w2 ",
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"run-length encode a string: multiple whitespace mixed in string",
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); # end: 1b34de62-e152-47be-bc88-469746df63b3
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cmp-ok( # begin: abf176e2-3fbd-40ad-bb2f-2dd6d4df721a
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rle-encode("aabbbcccc"),
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"eq",
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"2a3b4c",
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"run-length encode a string: lowercase characters",
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); # end: abf176e2-3fbd-40ad-bb2f-2dd6d4df721a
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cmp-ok( # begin: 7ec5c390-f03c-4acf-ac29-5f65861cdeb5
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rle-decode(""),
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"eq",
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"",
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"run-length decode a string: empty string",
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); # end: 7ec5c390-f03c-4acf-ac29-5f65861cdeb5
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cmp-ok( # begin: ad23f455-1ac2-4b0e-87d0-b85b10696098
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rle-decode("XYZ"),
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"eq",
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"XYZ",
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"run-length decode a string: single characters only",
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); # end: ad23f455-1ac2-4b0e-87d0-b85b10696098
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cmp-ok( # begin: 21e37583-5a20-4a0e-826c-3dee2c375f54
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rle-decode("2A3B4C"),
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"eq",
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"AABBBCCCC",
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"run-length decode a string: string with no single characters",
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); # end: 21e37583-5a20-4a0e-826c-3dee2c375f54
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cmp-ok( # begin: 1389ad09-c3a8-4813-9324-99363fba429c
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rle-decode("12WB12W3B24WB"),
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"eq",
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"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB",
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"run-length decode a string: single characters with repeated characters",
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); # end: 1389ad09-c3a8-4813-9324-99363fba429c
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cmp-ok( # begin: 3f8e3c51-6aca-4670-b86c-a213bf4706b0
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rle-decode("2 hs2q q2w2 "),
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"eq",
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" hsqq qww ",
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"run-length decode a string: multiple whitespace mixed in string",
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); # end: 3f8e3c51-6aca-4670-b86c-a213bf4706b0
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cmp-ok( # begin: 29f721de-9aad-435f-ba37-7662df4fb551
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rle-decode("2a3b4c"),
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"eq",
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"aabbbcccc",
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"run-length decode a string: lowercase string",
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); # end: 29f721de-9aad-435f-ba37-7662df4fb551
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cmp-ok( # begin: 2a762efd-8695-4e04-b0d6-9736899fbc16
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rle-decode(rle-encode("zzz ZZ zZ")),
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"eq",
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"zzz ZZ zZ",
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"encode and then decode: encode followed by decode gives original string",
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); # end: 2a762efd-8695-4e04-b0d6-9736899fbc16
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done-testing;

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