Add intergalactic transmission exercise

config.json

@@ -2713,6 +2713,18 @@
           "for-loops"
         ],
         "difficulty": 7
+      },
+      {
+        "slug": "intergalactic-transmission",
+        "name": "intergalactic-transmission",
+        "uuid": "845c8cf4-207c-438f-9d18-c5e7875ee729",
+        "practices": [
+          "bit-manipulation"
+        ],
+        "prerequisites": [
+          "bit-manipulation"
+        ],
+        "difficulty": 6
       }
     ],
     "foregone": [

exercises/Exercises.sln

@@ -1,4 +1,4 @@
-
+
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.0.31808.319
@@ -357,6 +357,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "StateOfTicTacToe", "practic
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BottleSong", "practice\bottle-song\BottleSong.csproj", "{6BD384E6-225E-4F8A-856C-3079957C6E36}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IntergalacticTransmission", "practice\intergalactic-transmission\IntergalacticTransmission.csproj", "{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -1063,6 +1065,10 @@ Global
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

exercises/practice/intergalactic-transmission/.docs/instructions.md

@@ -0,0 +1,37 @@
+# Instructions
+
+Your job is to help implement the message sequencer to add the parity bit to the messages and the decoder to receive messages.
+
+The entire message, itself, is sequence of a number of bytes.
+The transmitters and receivers can only transmit and receive one byte at a time, so parity bit needs to be added every eighth bit. 
+The algorithm for adding the bits is as follows:
+1. Divide the message bits into groups of 7, starting from the left (the message is transmitted from left to right).
+2. If the last group has less than 7 bits, append some 0s to pad the group to 7 bits.
+3. For each group, determine if there are an odd or even number of 1s.
+4. If the group has even number of 1s or none at all, append a 0 to the group. Otherwise, append 1 if there is odd number.
+
+For example, consider the message 0xC0_01_C0_DE.
+Writing this out in binary and locating every 7th bit:
+
+```text
+C    0    0    1    C    0    D    E
+1100_0000 0000_0001 1100_0000 1101_1110
+       ↑        ↑        ↑       ↑        (7th bits)
+```
+
+The last group has only 4 bits (0b1110), so three 0 bits are appended to make it 7 bits:
+
+```text
+| 1100_000 | 0000_000 | 0111_000 | 0001_101 | 1110_000 |
+```
+
+The first group contains two 1s (an even number of 1s), so 0 is appended to the group.
+The second group has none, so append 0.
+The rest have three, so they append 1.
+
+```text
+| 1100_0000 | 0000_0000 | 0111_0001 | 0001_1011 | 1110_0001 |
+| C    0    | 0    0    | 7    1    | 1    B    | E    1    |  (in hex)
+```
+
+Thus, the transmission sequence is 0xC0_00_71_1B_E1.

exercises/practice/intergalactic-transmission/.docs/introduction.md

@@ -0,0 +1,10 @@
+# Introduction
+
+Trillions upon trillions of messages are exchanged between Earth and the neighboring galaxies every millisecond. 
+But transmission over such long distances faces many obstacles.
+Pesky solar flares, worm holes, temporal distortions, stray forces, heck even the flap of a space butterfly wing can cause a random bit to flip during transmission.
+The difference between an "o" and a "k", a "[" and "{" or a cowboy emoji and a clown emoji can have huge ramifications, from missed orders to Galactic Stockmarket crashes.
+It is important for the receiver to know when the message has been corrupted so that the receiver can ask for the message to sent again.
+
+One day, an important message comes through.
+People have just heard about the legend about a way of transmitting in such a way that the receiver can tell when bit flipped ... the parity bit ...

exercises/practice/intergalactic-transmission/.editorconfig

@@ -0,0 +1,141 @@
+###############################
+# Core EditorConfig Options   #
+###############################
+
+; This file is for unifying the coding style for different editors and IDEs.
+; More information at:
+; https://docs.microsoft.com/en-us/visualstudio/ide/editorconfig-code-style-settings-reference?view=vs-2017
+; https://docs.microsoft.com/en-us/visualstudio/ide/create-portable-custom-editor-options?view=vs-2017
+
+root = true
+
+[*]
+indent_style = space
+
+[IntergalacticTransmission.cs]
+indent_size = 4
+
+###############################
+# .NET Coding Conventions     #
+###############################
+
+# Organize usings
+dotnet_sort_system_directives_first = true
+dotnet_separate_import_directive_groups = true
+
+# this. preferences
+dotnet_style_qualification_for_field = false:suggestion
+dotnet_style_qualification_for_property = false:suggestion
+dotnet_style_qualification_for_method = false:suggestion
+dotnet_style_qualification_for_event = false:suggestion
+
+# Language keywords vs BCL types preferences
+dotnet_style_predefined_type_for_locals_parameters_members = true:suggestion
+dotnet_style_predefined_type_for_member_access = true:suggestion
+
+# Parentheses preferences
+dotnet_style_parentheses_in_arithmetic_binary_operators = never_if_unnecessary:none
+dotnet_style_parentheses_in_relational_binary_operators = never_if_unnecessary:none
+dotnet_style_parentheses_in_other_binary_operators = never_if_unnecessary:none
+dotnet_style_parentheses_in_other_operators = never_if_unnecessary:suggestion
+
+# Modifier preferences
+dotnet_style_require_accessibility_modifiers = always:suggestion
+dotnet_style_readonly_field = true:suggestion
+
+# Expression-level preferences
+dotnet_style_object_initializer = true:suggestion
+dotnet_style_collection_initializer = true:suggestion
+dotnet_style_explicit_tuple_names = true:suggestion
+dotnet_style_prefer_inferred_tuple_names = true:suggestion
+dotnet_style_prefer_inferred_anonymous_type_member_names = true:suggestion
+dotnet_style_prefer_auto_properties = true:suggestion
+dotnet_style_prefer_is_null_check_over_reference_equality_method = true:suggestion
+dotnet_style_prefer_conditional_expression_over_assignment = true:suggestion
+dotnet_style_prefer_conditional_expression_over_return = true:suggestion
+dotnet_style_coalesce_expression = true:suggestion
+dotnet_style_null_propagation = true:suggestion
+
+###############################
+# Naming Conventions          #
+###############################
+
+# Style Definitions
+dotnet_naming_style.pascal_case_style.capitalization = pascal_case
+
+# Use PascalCase for constant fields
+dotnet_naming_rule.constant_fields_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.constant_fields_should_be_pascal_case.symbols = constant_fields
+dotnet_naming_rule.constant_fields_should_be_pascal_case.style = pascal_case_style
+dotnet_naming_symbols.constant_fields.applicable_kinds = field
+dotnet_naming_symbols.constant_fields.applicable_accessibilities = *
+dotnet_naming_symbols.constant_fields.required_modifiers = const
+
+###############################
+# C# Code Style Rules         #
+###############################
+
+# var preferences
+csharp_style_var_for_built_in_types = true:none
+csharp_style_var_when_type_is_apparent = true:none
+csharp_style_var_elsewhere = true:none
+
+# Expression-bodied members
+csharp_style_expression_bodied_methods = true:suggestion
+csharp_style_expression_bodied_constructors = true:suggestion
+csharp_style_expression_bodied_operators = true:suggestion
+csharp_style_expression_bodied_properties = true:suggestion
+csharp_style_expression_bodied_indexers = true:suggestion
+csharp_style_expression_bodied_accessors = true:suggestion
+
+# Pattern-matching preferences
+csharp_style_pattern_matching_over_is_with_cast_check = true:suggestion
+csharp_style_pattern_matching_over_as_with_null_check = true:suggestion
+
+# Null-checking preferences
+csharp_style_throw_expression = true:suggestion
+csharp_style_conditional_delegate_call = true:suggestion
+
+# Modifier preferences
+csharp_preferred_modifier_order = public,private,protected,internal,static,extern,new,virtual,abstract,sealed,override,readonly,unsafe,volatile,async:suggestion
+
+# Expression-level preferences
+csharp_prefer_braces = true:none
+csharp_prefer_simple_default_expression = true:suggestion
+csharp_style_deconstructed_variable_declaration = true:suggestion
+csharp_style_pattern_local_over_anonymous_function = true:suggestion
+csharp_style_inlined_variable_declaration = true:suggestion
+
+###############################
+# C# Formatting Rules         #
+###############################
+
+# New line preferences
+csharp_new_line_before_open_brace = all
+csharp_new_line_before_else = true
+csharp_new_line_before_catch = true
+csharp_new_line_before_finally = true
+csharp_new_line_before_members_in_object_initializers = false
+csharp_new_line_before_members_in_anonymous_types = false
+csharp_new_line_between_query_expression_clauses = true
+
+# Indentation preferences
+csharp_indent_case_contents = true
+csharp_indent_switch_labels = true
+csharp_indent_labels = flush_left
+
+# Space preferences
+csharp_space_after_cast = false
+csharp_space_after_keywords_in_control_flow_statements = true
+csharp_space_between_method_declaration_parameter_list_parentheses = false
+csharp_space_between_method_call_parameter_list_parentheses = false
+csharp_space_before_colon_in_inheritance_clause = true
+csharp_space_after_colon_in_inheritance_clause = true
+csharp_space_around_binary_operators = before_and_after
+csharp_space_between_method_declaration_empty_parameter_list_parentheses = false
+csharp_space_between_method_call_name_and_opening_parenthesis = false
+csharp_space_between_method_call_empty_parameter_list_parentheses = false
+
+# Wrapping preferences
+csharp_preserve_single_line_blocks = true
+csharp_preserve_single_line_statements = true

exercises/practice/intergalactic-transmission/.meta/Example.cs

@@ -0,0 +1,91 @@
+public static class IntergalacticTransmission
+{
+    private const byte InitUpperMask = (byte)0xFE;
+
+    public static byte[] GetTransmitSequence(byte[] message)
+    {
+        List<byte> transmitSeq = new List<byte>();
+        byte carry = 0;
+        byte upperMask = InitUpperMask;
+
+        for (int i = 0; i < message.Length; i++)
+        {
+            if (upperMask == 0)
+            {
+                // The carry now contains 7 bits. Flush the carry out.
+                transmitSeq.Add(AddParity(carry));
+                carry = 0;
+                upperMask = 0xFE;
+            }
+
+            int shiftPlaces = byte.TrailingZeroCount(upperMask);
+            int current = (carry << (8 - shiftPlaces)) | (message[i] >>> shiftPlaces);
+            transmitSeq.Add(AddParity((byte)current));
+
+            // Update parameters for next round.
+            carry = (byte)(message[i] & (~upperMask));
+
+            // Shorten the upper mask.
+            upperMask = (byte)(upperMask << 1);
+        }
+
+        if (upperMask != InitUpperMask)
+        {
+            byte lastGroup = (byte)(carry << byte.PopCount(upperMask));
+            // We have left over carry data
+            transmitSeq.Add(AddParity(lastGroup));
+        }
+        return transmitSeq.ToArray();
+    }
+
+    private static byte AddParity(byte source)
+    {
+        if (byte.PopCount((byte)(source & 0x7F)) % 2 == 0)
+        {
+            return (byte)(source << 1);
+        }
+        return (byte)((source << 1) | 1);
+    }
+
+    public static byte[] DecodeSequence(byte[] receivedSeq)
+    {
+        if (receivedSeq.Length == 0)
+        {
+            return [];
+        }
+
+        List<byte> decodedMessage = new List<byte>();
+        byte byteToAdd = 0x00;
+        byte upperMask = 0xFF;
+        for (int i = 0; i < receivedSeq.Length; i++)
+        {
+            if (upperMask == 0xFF)
+            {
+                // We've completed a complete round.
+                // Current byte too short.
+                byteToAdd = GetByteData(receivedSeq[i]);
+                upperMask = 0x80;
+                continue;
+            }
+
+            byte currentByteData = GetByteData(receivedSeq[i]);
+            byte contribution = (byte)(currentByteData >>> byte.TrailingZeroCount(upperMask));
+            decodedMessage.Add((byte)(byteToAdd | contribution));
+
+            // Update parameters for next round
+            byteToAdd = (byte)((currentByteData & ~(upperMask | 0x01)) << byte.PopCount(upperMask));
+            upperMask = (byte)((upperMask >> 1) | 0x80);
+        }
+        return decodedMessage.ToArray();
+    }
+
+    private static byte GetByteData(byte data)
+    {
+        if (byte.PopCount(data) % 2 != 0)
+        {
+            throw new ArgumentException("Byte has incorrect parity");
+        }
+
+        return (byte)(data & 0xFE);
+    }
+}

exercises/practice/intergalactic-transmission/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "IntergalacticTransmission.cs"
+    ],
+    "test": [
+      "IntergalacticTransmissionTests.cs"
+    ],
+    "example": [
+      ".meta/Example.cs"
+    ]
+  },
+  "blurb": "Help detect errors in transmissions to neighboring galaxies"
+}

exercises/practice/intergalactic-transmission/IntergalacticTransmission.cs

@@ -0,0 +1,12 @@
+public static class IntergalacticTransmission
+{
+    public static byte[] GetTransmitSequence(byte[] message)
+    {
+        throw new NotImplementedException("You need to implement this method.");
+    }
+
+    public static byte[] DecodeSequence(byte[] receivedSeq)
+    {
+        throw new NotImplementedException("You need to implement this method.");
+    }
+}

exercises/practice/intergalactic-transmission/IntergalacticTransmission.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
+  </PropertyGroup>
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="xunit.v3" Version="1.1.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1" />
+    <PackageReference Include="Exercism.Tests.xunit.v3" Version="0.1.0-beta1" />
+  </ItemGroup>
+</Project>