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ErikSchierboomErikSchierboom
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Add baffling-birthdays 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": "baffling-birthdays",
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"name": "baffling-birthdays",
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"uuid": "f75d1dd2-63ee-4258-a4e9-f208fb8e8bd4",
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"practices": [],
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"prerequisites": [],
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"difficulty": 5
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}
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],
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"foregone": [

‎exercises/Exercises.sln‎

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@@ -357,6 +357,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "StateOfTicTacToe", "practic
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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}") = "BafflingBirthdays", "practice\baffling-birthdays\BafflingBirthdays.csproj", "{9D596842-830C-417D-807A-6B910EE467B4}"
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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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{9D596842-830C-417D-807A-6B910EE467B4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{9D596842-830C-417D-807A-6B910EE467B4}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{9D596842-830C-417D-807A-6B910EE467B4}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{9D596842-830C-417D-807A-6B910EE467B4}.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
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{8E276065-1371-4CFA-BA20-95225EC6AEBC} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{67E9BAB3-9805-42F1-9298-E9BBB795140E} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{6BD384E6-225E-4F8A-856C-3079957C6E36} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{9D596842-830C-417D-807A-6B910EE467B4} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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EndGlobalSection
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GlobalSection(ExtensibilityGlobals) = postSolution
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SolutionGuid = {AB4EA6C9-5461-4024-BDC7-2AE0C3A85CD1}

‎exercises/practice/baffling-birthdays/.docs/instructions.md‎

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# Instructions
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Your task is to implement a solution that verifies the Birthday Problem's probabilities.
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To do this, you need to:
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- Determine if two birthdates match (same month and day).
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- Generate random birthdates.
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- Check if a set of randomly generated birthdates contains at least one matching pair.
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- Calculate the probability of at least one match for different group sizes.
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```exercism/caution
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The Birthday Problem assumes that birthdays are uniformly distributed within a single year.
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While the year should vary between different random birthdate generation calls, all birthdates within a single call must share the same year.
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```

‎exercises/practice/baffling-birthdays/.docs/introduction.md‎

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# Introduction
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Fresh out of graduation, you're throwing a huge party to celebrate with friends and family.
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Over 70 people have shown up, including your mildly eccentric Uncle Ted.
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In one of his usual antics, he bets you £100 that at least two people in the room share the same birthday.
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That sounds ridiculous—there are 365 possible birthdays, so you confidently accept.
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To your astonishment, after collecting just 32 birthdays, you've already found a match.
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Magnanimous, you hand Uncle Ted his £100, but something feels off.
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The next day, curiosity gets the better of you.
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A quick web search leads you to the [Birthday Problem][birthday-problem], which reveals that with just 23 people, the probability of a shared birthday exceeds 50%.
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Ah. So _that's_ why Uncle Ted was so confident.
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Determined to turn the tables, you start looking up other paradoxes—next time, _you'll_ be the one making the bets.
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```exercism/note
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The birthday paradox is a veridical paradox: even though it feels wrong, it is actually true.
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[veridical-paradox]: https://en.wikipedia.org/wiki/Paradox#Quine's_classification
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```
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[birthday-problem]: https://en.wikipedia.org/wiki/Birthday_problem

‎exercises/practice/baffling-birthdays/.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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[BafflingBirthdays.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/baffling-birthdays/.meta/Example.cs‎

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‎exercises/practice/baffling-birthdays/.meta/config.json‎

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{
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"authors": [
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"erikschierboom"
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],
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"files": {
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"solution": [
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"BafflingBirthdays.cs"
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],
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"test": [
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"BafflingBirthdaysTests.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": ""
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}

‎exercises/practice/baffling-birthdays/BafflingBirthdays.cs‎

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public static class BafflingBirthdays
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{
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public static bool MatchingBirthday(DateOnly birthday1, DateOnly birthday2) =>
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birthday1.Month == birthday2.Month && birthday1.Day == birthday2.Day;
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private static DateOnly RandomBirthdate(int year)
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{
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var month = Random.Shared.Next(1, 12 + 1);
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var day = Random.Shared.Next(1, DateTime.DaysInMonth(year, month) + 1);
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return new DateOnly(year, month, day);
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}
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public static DateOnly[] RandomBirthdates(int numberOfBirthdays)
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{
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var year = Random.Shared.Next(1900, DateTime.Now.Year + 1);
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return Enumerable.Range(0, numberOfBirthdays).Select(_ => RandomBirthdate(year)).ToArray();
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}
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public static bool HasMatchingBirthdays(DateOnly[] birthdays) =>
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birthdays
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.SelectMany((birthday, i) => birthdays.Skip(i + 1), MatchingBirthday)
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.Any(matching => matching);
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public static double LikelihoodHasMatchingBirthday(int numberOfBirthdays)
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{
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var matchingBirthdayIterationCount = 0;
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for (var i = 0; i < 10000; i++)
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{
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if (HasMatchingBirthdays(RandomBirthdates(numberOfBirthdays)))
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matchingBirthdayIterationCount++;
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}
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return matchingBirthdayIterationCount / 100.0;
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}
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}

‎exercises/practice/baffling-birthdays/BafflingBirthdays.csproj‎

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<ImplicitUsings>enable</ImplicitUsings>
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<Nullable>enable</Nullable>
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<OutputType>Exe</OutputType>
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<TargetFramework>net8.0</TargetFramework>
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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="3.0.2" />
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</ItemGroup>
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</Project>

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