Add run-length-encoding (#559)

config.json

@@ -731,6 +731,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "run-length-encoding",
+        "name": "Run-Length Encoding",
+        "uuid": "9c53981f-b75e-4782-be4a-3b13e1d40fb3",
+        "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": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "lib/run_length_encoding.dart"
+    ],
+    "test": [
+      "test/run_length_encoding_test.dart"
+    ],
+    "example": [
+      ".meta/lib/example.dart"
+    ]
+  },
+  "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/lib/example.dart

@@ -0,0 +1,11 @@
+class RunLengthEncoder {
+  String encode(String plaintext) {
+    return plaintext.replaceAllMapped(
+        RegExp(r'(.)\1+'), (Match m) => m[0]!.length.toString() + m[1]!);
+  }
+
+  String decode(String ciphertext) {
+    return ciphertext.replaceAllMapped(
+        RegExp(r'(\d+)(.)'), (Match m) => m[2]! * int.parse(m[1]!));
+  }
+}

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/analysis_options.yaml

@@ -0,0 +1,18 @@
+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+  errors:
+    unused_element:        error
+    unused_import:         error
+    unused_local_variable: error
+    dead_code:             error
+
+linter:
+  rules:
+    # Error Rules
+    - avoid_relative_lib_imports
+    - avoid_types_as_parameter_names
+    - literal_only_boolean_expressions
+    - no_adjacent_strings_in_list
+    - valid_regexps

exercises/practice/run-length-encoding/lib/run_length_encoding.dart

@@ -0,0 +1,3 @@
+class RunLengthEncoder {
+  // Put your code here
+}

exercises/practice/run-length-encoding/pubspec.yaml

@@ -0,0 +1,5 @@
+name: 'run_length_encoding'
+environment:
+  sdk: '>=3.2.0 <4.0.0'
+dev_dependencies:
+  test: '<2.0.0'

exercises/practice/run-length-encoding/test/run_length_encoding_test.dart

@@ -0,0 +1,77 @@
+import 'package:run_length_encoding/run_length_encoding.dart';
+import 'package:test/test.dart';
+
+void main() {
+  final rle = RunLengthEncoder();
+
+  group('Encoding', () {
+    test('empty string', () {
+      final encoded = rle.encode("");
+      expect(encoded, equals(""));
+    }, skip: false);
+
+    test('single characters only are encoded without count', () {
+      final encoded = rle.encode("XYZ");
+      expect(encoded, equals("XYZ"));
+    }, skip: true);
+
+    test('string with no single characters', () {
+      final encoded = rle.encode("AABBBCCCC");
+      expect(encoded, equals("2A3B4C"));
+    }, skip: true);
+
+    test('single characters mixed with repeated characters', () {
+      final encoded = rle.encode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB");
+      expect(encoded, equals("12WB12W3B24WB"));
+    }, skip: true);
+
+    test('multiple whitespace mixed in string', () {
+      final encoded = rle.encode("  hsqq qww  ");
+      expect(encoded, equals("2 hs2q q2w2 "));
+    }, skip: true);
+
+    test('lowercase characters', () {
+      final encoded = rle.encode("aabbbcccc");
+      expect(encoded, equals("2a3b4c"));
+    }, skip: true);
+  });
+
+  group('Decoding', () {
+    test('empty string', () {
+      final decoded = rle.decode("");
+      expect(decoded, equals(""));
+    }, skip: true);
+
+    test('single characters only', () {
+      final decoded = rle.decode("XYZ");
+      expect(decoded, equals("XYZ"));
+    }, skip: true);
+
+    test('string with no single characters', () {
+      final decoded = rle.decode("2A3B4C");
+      expect(decoded, equals("AABBBCCCC"));
+    }, skip: true);
+
+    test('single characters with repeated characters', () {
+      final decoded = rle.decode("12WB12W3B24WB");
+      expect(decoded, equals("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"));
+    }, skip: true);
+
+    test('multiple whitespace mixed in string', () {
+      final decoded = rle.decode("2 hs2q q2w2 ");
+      expect(decoded, equals("  hsqq qww  "));
+    }, skip: true);
+
+    test('lowercase string', () {
+      final decoded = rle.decode("2a3b4c");
+      expect(decoded, equals("aabbbcccc"));
+    }, skip: true);
+  });
+
+  group('Encode then Decode', () {
+    test('encode followed by decode gives original string', () {
+      final input = "zzz ZZ  zZ";
+      expect(rle.decode(rle.encode(input)), equals(input));
+    }, skip: true);
+  });
+}