Add run-length-encoding exercise

config.json

@@ -776,6 +776,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "run-length-encoding",
+        "name": "Run-Length Encoding",
+        "uuid": "e39b5e8b-cd91-4adf-bb1e-015367ef4f8c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },

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

@@ -0,0 +1,20 @@
+# 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.

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "run-length-encoding.R"
+    ],
+    "test": [
+      "test_run-length-encoding.R"
+    ],
+    "example": [
+      ".meta/example.R"
+    ]
+  },
+  "blurb": "Implement run-length encoding and decoding.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Run-length_encoding"
+}

exercises/practice/run-length-encoding/.meta/example.R

@@ -0,0 +1,22 @@
+library(stringr)
+
+encode <- function(plaintext) {
+  runs <- str_match_all(plaintext, "(.)\\1*")[[1]]
+  apply(runs, 1, encode_run) |> paste0(collapse = "")
+}
+
+encode_run <- function(run) {
+  num_chars <- nchar(run[1])
+  prefix <- ifelse(num_chars == 1, "", num_chars |> as.character())
+  paste(prefix, run[2], sep = "")
+}
+
+decode <- function(ciphertext) {
+  runs <- str_match_all(ciphertext, "(\\d+)?(.)")[[1]]
+  apply(runs, 1, decode_run) |> paste0(collapse = "")
+}
+
+decode_run <- function(run) {
+  count <- ifelse(is.na(run[2]), 1, run[2] |> as.numeric())
+  str_dup(run[3], count)
+}

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

@@ -0,0 +1,49 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[ad53b61b-6ffc-422f-81a6-61f7df92a231]
+description = "run-length encode a string -> empty string"
+
+[52012823-b7e6-4277-893c-5b96d42f82de]
+description = "run-length encode a string -> single characters only are encoded without count"
+
+[b7868492-7e3a-415f-8da3-d88f51f80409]
+description = "run-length encode a string -> string with no single characters"
+
+[859b822b-6e9f-44d6-9c46-6091ee6ae358]
+description = "run-length encode a string -> single characters mixed with repeated characters"
+
+[1b34de62-e152-47be-bc88-469746df63b3]
+description = "run-length encode a string -> multiple whitespace mixed in string"
+
+[abf176e2-3fbd-40ad-bb2f-2dd6d4df721a]
+description = "run-length encode a string -> lowercase characters"
+
+[7ec5c390-f03c-4acf-ac29-5f65861cdeb5]
+description = "run-length decode a string -> empty string"
+
+[ad23f455-1ac2-4b0e-87d0-b85b10696098]
+description = "run-length decode a string -> single characters only"
+
+[21e37583-5a20-4a0e-826c-3dee2c375f54]
+description = "run-length decode a string -> string with no single characters"
+
+[1389ad09-c3a8-4813-9324-99363fba429c]
+description = "run-length decode a string -> single characters with repeated characters"
+
+[3f8e3c51-6aca-4670-b86c-a213bf4706b0]
+description = "run-length decode a string -> multiple whitespace mixed in string"
+
+[29f721de-9aad-435f-ba37-7662df4fb551]
+description = "run-length decode a string -> lowercase string"
+
+[2a762efd-8695-4e04-b0d6-9736899fbc16]
+description = "encode and then decode -> encode followed by decode gives original string"

exercises/practice/run-length-encoding/run-length-encoding.R

@@ -0,0 +1,7 @@
+encode <- function(plaintext) {
+
+}
+
+decode <- function(ciphertext) {
+
+}

exercises/practice/run-length-encoding/test_run-length-encoding.R

@@ -0,0 +1,60 @@
+source("./run-length-encoding.R")
+library(testthat)
+
+test_that("Encode empty string", {
+  expect_equal(encode(""), "")
+})
+
+test_that("Encode single characters only are encoded without count", {
+  expect_equal(encode("XYZ"), "XYZ")
+})
+
+test_that("Encode string with no single characters", {
+  expect_equal(encode("AABBBCCCC"), "2A3B4C")
+})
+
+test_that("Encode single characters mixed with repeated characters", {
+  expect_equal(
+    encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"),
+    "12WB12W3B24WB"
+  )
+})
+
+test_that("Encode multiple whitespace mixed in string", {
+  expect_equal(encode("  hsqq qww  "), "2 hs2q q2w2 ")
+})
+
+test_that("Encode lowercase characters", {
+  expect_equal(encode("aabbbcccc"), "2a3b4c")
+})
+
+test_that("Decode empty string", {
+  expect_equal(decode(""), "")
+})
+
+test_that("Decode single characters only", {
+  expect_equal(decode("XYZ"), "XYZ")
+})
+
+test_that("Decode string with no single characters", {
+  expect_equal(decode("2A3B4C"), "AABBBCCCC")
+})
+
+test_that("Decode single characters with repeated characters", {
+  expect_equal(
+    decode("12WB12W3B24WB"),
+    "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
+  )
+})
+
+test_that("Decode multiple whitespace mixed in string", {
+  expect_equal(decode("2 hs2q q2w2 "), "  hsqq qww  ")
+})
+
+test_that("Decode lowercase string", {
+  expect_equal(decode("2a3b4c"), "aabbbcccc")
+})
+
+test_that("Encode followed by decode gives original string", {
+  expect_equal("zzz ZZ  zZ" |> encode() |> decode(), "zzz ZZ  zZ")
+})