Add intergalactic transmission exercise (#2398)

* Add intergalactic transmission exercise

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

Co-authored-by: Erik Schierboom <[email protected]>

* Adjust tests

* Sync intergalactic transmission with problem specs

* Add missing prerequisites

Co-authored-by: Erik Schierboom <[email protected]>

* Remove sln file

* Fix Exercises.sln

---------

Co-authored-by: Erik Schierboom <[email protected]>

Author: kahgoh

config.json

@@ -2714,6 +2714,23 @@
         ],
         "difficulty": 7
       },
+      {
+        "slug": "intergalactic-transmission",
+        "name": "intergalactic-transmission",
+        "uuid": "845c8cf4-207c-438f-9d18-c5e7875ee729",
+        "practices": [
+          "bit-manipulation"
+        ],
+        "prerequisites": [
+          "bit-manipulation",
+          "arrays",
+          "exceptions",
+          "integral-numbers",
+          "for-loops",
+          "if-statements"
+        ],
+        "difficulty": 6
+      },
       {
         "slug": "split-second-stopwatch",
         "name": "Split-Second Stopwatch",

exercises/Exercises.sln

@@ -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
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SplitSecondStopwatch", "practice\split-second-stopwatch\SplitSecondStopwatch.csproj", "{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}"
 EndProject
 Global
@@ -2469,18 +2471,18 @@ Global
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Release|x64.Build.0 = Release|Any CPU
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Release|x86.ActiveCfg = Release|Any CPU
 		{6BD384E6-225E-4F8A-856C-3079957C6E36}.Release|x86.Build.0 = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|x64.ActiveCfg = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|x64.Build.0 = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Debug|x86.Build.0 = Debug|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|Any CPU.Build.0 = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|x64.ActiveCfg = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|x64.Build.0 = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|x86.ActiveCfg = Release|Any CPU
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692}.Release|x86.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}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Debug|x64.Build.0 = Debug|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Debug|x86.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
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|x64.ActiveCfg = Release|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|x64.Build.0 = Release|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|x86.ActiveCfg = Release|Any CPU
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5}.Release|x86.Build.0 = Release|Any CPU
 		{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Debug|x64.ActiveCfg = Debug|Any CPU
@@ -2673,9 +2675,8 @@ Global
 		{8E276065-1371-4CFA-BA20-95225EC6AEBC} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
 		{67E9BAB3-9805-42F1-9298-E9BBB795140E} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
 		{6BD384E6-225E-4F8A-856C-3079957C6E36} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
-		{DA4856F5-A260-43A0-9C9C-6DD2E2B08692} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
-		{B587F905-CC4E-0FB1-25B1-84C433FD33E0} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
-		{0A6CD51A-2120-4A72-A17B-08CCC2E6D365} = {B587F905-CC4E-0FB1-25B1-84C433FD33E0}
+		{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
+		{0A6CD51A-2120-4A72-A17B-08CCC2E6D365} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {AB4EA6C9-5461-4024-BDC7-2AE0C3A85CD1}

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

@@ -0,0 +1,54 @@
+# Instructions
+
+Your job is to help implement
+
+- the transmitter, which calculates the transmission sequence, and
+- the receiver, which decodes it.
+
+A parity bit is simple way of detecting transmission errors.
+The transmitters and receivers can only transmit and receive _exactly_ eight bits at a time (including the parity bit).
+The parity bit is set so that there is an _even_ number 1s in each transmission and is always the first bit from the right.
+So if the receiver receives `11000001`, `01110101` or `01000000` (i.e. a transmission with an odd number of 1 bits), it knows there is an error.
+
+However, messages are rarely this short, and need to be transmitted in a sequence when they are longer.
+
+For example, consider the message `11000000 00000001 11000000 11011110` (or `C0 01 C0 DE` in hex).
+
+Since each transmission contains exactly eight bits, it can only contain seven bits of data and the parity bit.
+A parity bit must then be inserted after every seven bits of data:
+
+```text
+11000000 00000001 11000000 11011110
+      ↑       ↑       ↑       ↑          (7th bits)
+```
+
+The transmission sequence for this message looks like this:
+
+```text
+1100000_ 0000000_ 0111000_ 0001101_ 1110
+       ↑        ↑        ↑        ↑      (parity bits)
+```
+
+The data in the first transmission in the sequence (`1100000`) has two 1 bits (an even number), so the parity bit is 0.
+The first transmission becomes `11000000` (or `C0` in hex).
+
+The data in the next transmission (`0000000`) has zero 1 bits (an even number again), so the parity bit is 0 again.
+The second transmission thus becomes `00000000` (or `00` in hex).
+
+The data for the next two transmissions (`0111000` and `0001101`) have three 1 bits.
+Their parity bits are set to 1 so that they have an even number of 1 bits in the transmission.
+They are transmitted as `01110001` and `00011011` (or `71` and `1B` in hex).
+
+The last transmission (`1110`) has only four bits of data.
+Since exactly eight bits are transmitted at a time and the parity bit is the right most bit, three 0 bits and then the parity bit are added to make up eight bits.
+It now looks like this (where `_` is the parity bit):
+
+```text
+1110 000_
+     ↑↑↑   (added 0 bits)
+```
+
+There is an odd number of 1 bits again, so the parity bit is 1.
+The last transmission in the sequence becomes `11100001` (or `E1` in hex).
+
+The entire transmission sequence for this message is `11000000 00000000 01110001 00011011 11100001` (or `C0 00 71 1B E1` in hex).

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

@@ -0,0 +1,23 @@
+# Introduction
+
+Trillions upon trillions of messages zip between Earth and neighboring galaxies every millisecond.
+But transmitting over such long distances is tricky.
+Pesky solar flares, temporal distortions, stray forces, and even the flap of a space butterfly's wing can cause a random bit to change during transmission.
+
+Now imagine the consequences:
+
+- Crashing the Intergalactic Share Market when "buy low" turns to "sell now".
+- Losing contact with the Kepler Whirl system when "save new worm hole" becomes "cave new worm hole".
+- Or plunging the universe into existential horror by replacing a cowboy emoji 🤠 with a clown emoji 🤡.
+
+Detecting corrupted messages isn't just important — it's critical.
+The receiver _must_ know when something has gone wrong before disaster strikes.
+
+But how?
+Scientists and engineers from across the universe have been battling this problem for eons.
+Entire cosmic AI superclusters churn through the data.
+And then, one day, a legend resurfaces — an ancient, powerful method, whispered in debugging forums, muttered by engineers who've seen too much...
+
+The Parity Bit!
+
+A method so simple, so powerful, that it might just save interstellar communication.

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);
+    }
+}