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Add intergalactic transmission exercise
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‎config.json‎

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

‎exercises/Exercises.sln‎

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

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

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

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

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# Introduction
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Trillions upon trillions of messages are exchanged between Earth and the neighboring galaxies every millisecond.
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But transmission over such long distances faces many obstacles.
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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.
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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.
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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.
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One day, an important message comes through.
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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

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

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

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

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

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

‎exercises/practice/intergalactic-transmission/IntergalacticTransmission.cs‎

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public static class IntergalacticTransmission
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{
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public static byte[] GetTransmitSequence(byte[] message)
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{
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throw new NotImplementedException("You need to implement this method.");
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}
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public static byte[] DecodeSequence(byte[] receivedSeq)
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{
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throw new NotImplementedException("You need to implement this method.");
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}
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}

‎exercises/practice/intergalactic-transmission/IntergalacticTransmission.csproj‎

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

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