Add run-length-encoding (#329)

Author: BNAndras

config.json

@@ -589,6 +589,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "run-length-encoding",
+        "name": "Run-Length Encoding",
+        "uuid": "b496f1b1-c04e-4d13-95bf-507bf3e616a7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "spiral-matrix",
         "name": "Spiral Matrix",

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": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "run-length-encoding.coffee"
+    ],
+    "test": [
+      "run-length-encoding.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "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.coffee

@@ -0,0 +1,12 @@
+class RunLengthEncoding
+  @encode: (string) ->
+    consecutiveChars = /([\w\s])\1*/g
+    string.replace consecutiveChars, (match) ->
+      if match.length > 1 then match.length + match[0] else match[0]
+
+  @decode: (string) ->
+    countAndChar = /(\d+)(\w|\s)/g
+    string.replace countAndChar, (_, count, char) ->
+      char.repeat count
+
+module.exports = RunLengthEncoding

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.coffee

@@ -0,0 +1,6 @@
+class RunLengthEncoding
+  @encode: (string) ->
+
+  @decode: (string) ->
+
+module.exports = RunLengthEncoding

exercises/practice/run-length-encoding/run-length-encoding.spec.coffee

@@ -0,0 +1,70 @@
+RLE = require './run-length-encoding'
+
+describe 'Run Length Encoding', ->
+  describe 'encode', ->
+    it 'empty string', ->
+      input = ''
+      expected = ''
+      expect(RLE.encode input).toEqual expected
+
+    xit 'single characters only are encoded without count', ->
+      input = 'XYZ'
+      expected = 'XYZ'
+      expect(RLE.encode input).toEqual expected
+
+    xit 'string with no single characters', ->
+      input = 'AABBBCCCC'
+      expected = '2A3B4C'
+      expect(RLE.encode input).toEqual expected
+
+    xit 'string with single characters mixed with repeated characters', ->
+      input = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB'
+      expected = '12WB12W3B24WB'
+      expect(RLE.encode input).toEqual expected
+    
+    xit 'string with multiple whitespace mixed', ->
+      input = '  hsqq qww  '
+      expected = '2 hs2q q2w2 '
+      expect(RLE.encode input).toEqual expected
+    
+    xit 'string with lowercase characters', ->
+      input = 'aabbbcccc'
+      expected = '2a3b4c'
+      expect(RLE.encode input).toEqual expected
+    
+  describe 'decode', ->
+    xit 'empty string', ->
+      input = ''
+      expected = ''
+      expect(RLE.decode input).toEqual expected
+
+    xit 'string with single characters only', ->
+      input = 'XYZ'
+      expected = 'XYZ'
+      expect(RLE.decode input).toEqual expected
+
+    xit 'string with no single characters', ->
+      input = '2A3B4C'
+      expected = 'AABBBCCCC'
+      expect(RLE.decode input).toEqual expected
+
+    xit 'string with single characters mixed with repeated characters', ->
+      input = '12WB12W3B24WB'
+      expected = 'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB'
+      expect(RLE.decode input).toEqual expected
+
+    xit 'string with multiple whitespaces', ->
+      input = '2 hs2q q2w2 '
+      expected = '  hsqq qww  '
+      expect(RLE.decode input).toEqual expected
+
+    xit 'string with lowercase characters', ->
+      input = '2a3b4c'
+      expected = 'aabbbcccc'
+      expect(RLE.decode input).toEqual expected
+  
+  xit 'encode followed by decode gives original string', ->
+    plainText = 'zzz ZZ  zZ'
+    input = RLE.encode plainText
+    expected = 'zzz ZZ  zZ'
+    expect(RLE.decode input).toEqual expected