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ErikSchierboomErikSchierboom
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Add baffling-birthdays exercise
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‎config.json‎

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"datetimes",
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"classes"
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],
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"difficulty": 6
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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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"randomness",
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"datetimes"
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],
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"prerequisites": [
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"datetimes",
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"randomness",
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"numbers"
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],
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"difficulty": 5
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}
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],

‎exercises/Exercises.sln‎

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@@ -361,6 +361,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IntergalacticTransmission",
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EndProject
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SplitSecondStopwatch", "practice\split-second-stopwatch\SplitSecondStopwatch.csproj", "{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}"
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EndProject
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BafflingBirthdays", "practice\baffling-birthdays\BafflingBirthdays.csproj", "{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}"
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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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{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Release|x64.Build.0 = Release|Any CPU
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{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Release|x86.ActiveCfg = Release|Any CPU
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{0A6CD51A-2120-4A72-A17B-08CCC2E6D365}.Release|x86.Build.0 = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|x64.ActiveCfg = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|x64.Build.0 = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|x86.ActiveCfg = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Debug|x86.Build.0 = Debug|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|Any CPU.Build.0 = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|x64.ActiveCfg = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|x64.Build.0 = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|x86.ActiveCfg = Release|Any CPU
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E}.Release|x86.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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{6BD384E6-225E-4F8A-856C-3079957C6E36} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{E81F1BA3-1F99-4DCB-B875-78D1F4750BD5} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{0A6CD51A-2120-4A72-A17B-08CCC2E6D365} = {E276EF69-669A-43E0-88AC-8ABB17A9C026}
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{1BA5F72A-ED8E-48A8-8FD6-0F567BDCBD9E} = {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 estimate the birthday paradox's probabilities.
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To do this, you need to:
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- Generate random birthdates.
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- Check if a collection of randomly generated birthdates contains at least two with the same birthday.
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- Estimate the probability that at least two people in a group share the same birthday for different group sizes.
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~~~~exercism/note
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A birthdate includes the full date of birth (year, month, and day), whereas a birthday refers only to the month and day, which repeat each year.
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Two birthdates with the same month and day correspond to the same birthday.
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~~~~
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~~~~exercism/caution
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The birthday paradox assumes that:
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- There are 365 possible birthdays (no leap years).
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- Each birthday is equally likely (uniform distribution).
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Your implementation must follow these assumptions.
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~~~~

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

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# Introduction
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Fresh out of college, 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 many more possible birthdays than there are guests, so you confidently accept.
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To your astonishment, after collecting the birthdays of just 32 guests, you've already found two guests that share the same birthday.
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Accepting your loss, 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 paradox][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][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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public static class BafflingBirthdays
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{
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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 SharedBirthday(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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private static bool MatchingBirthday(DateOnly birthday1, DateOnly birthday2) =>
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birthday1.Month == birthday2.Month && birthday1.Day == birthday2.Day;
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public static double EstimatedProbabilityOfSharedBirthday(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 (SharedBirthday(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/.meta/Generator.tpl‎

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{{ func to_dateonly
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parts = string.split $0 "-"
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year = parts[0] | string.to_int
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month = parts[1] | string.to_int
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day = parts[2] | string.to_int
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$"new({year}, {month}, {day})"
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end }}
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public class {{ testClass }}
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{
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{{- for test in tests }}
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[Fact{{ if !for.first }}(Skip = "Remove this Skip property to run this test"){{ end }}]
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public void {{ test.testMethod }}()
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{
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{{- if test.property == "sharedBirthday" }}
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DateOnly[] birthdates = [
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{{- for birthdate in test.input.birthdates }}
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{{ birthdate | to_dateonly }}{{- if !for.last }},{{ end -}}
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{{ end }}
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];
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Assert.{{ test.expected ? "True" : "False" }}({{ testedClass }}.{{ test.testedMethod }}(birthdates));
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{{- else if test.property == "randomBirthdates" }}
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{{-if test.expected.years }}
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var uniqueRandomYears = {{ testedClass }}.{{ test.testedMethod }}(50)
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.Select(birthdate => birthdate.Year)
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.ToHashSet();
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Assert.All(uniqueRandomYears, year => Assert.False(DateTime.IsLeapYear(year)));
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{{- else if test.expected.months }}
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var uniqueRandomMonths = {{ testedClass }}.{{ test.testedMethod }}(100)
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.Select(birthdate => birthdate.Month)
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.ToHashSet();
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Assert.Equal(12, uniqueRandomMonths.Count);
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{{- else if test.expected.days }}
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var uniqueRandomDays = {{ testedClass }}.{{ test.testedMethod }}(300)
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.Select(birthdate => birthdate.Day)
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.ToHashSet();
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Assert.Equal(31, uniqueRandomDays.Count);
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{{- else }}
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for (var count = 1; count < 10; count++)
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{
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var randomBirthdates = {{ testedClass }}.{{ test.testedMethod }}(count);
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Assert.Equal(count, randomBirthdates.Length);
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}
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{{ end -}}
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{{- else if test.property == "estimatedProbabilityOfSharedBirthday" }}
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Assert.Equal({{ test.expected }}, {{ testedClass }}.{{ test.testedMethod }}({{ test.input.groupSize }}), tolerance: 1.0);
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{{ end -}}
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}
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{{ end -}}
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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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"invalidator": [
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"BafflingBirthdays.csproj"
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]
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},
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"blurb": "Estimate the birthday paradox's probabilities.",
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"source": "Erik Schierboom",
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"source_url": "https://github.com/exercism/problem-specifications/pull/2539"
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}

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