Add baffling-birthdays exercise

exercises/baffling-birthdays/canonical-data.json

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+{
+  "exercise": "baffling-birthdays",
+  "comments": [
+    "Dates are formatted as 'YYYY-MM-DD'.",
+    "",
+    "To increase the likelihood of consistent result, the tests should run the code returning random results many times.",
+    "",
+    "The expected probability values should be compared using some tolerance to allow for small deviations."
+  ],
+  "cases": [
+    {
+      "uuid": "f7b3eb26-bcfc-4c1e-a2de-af07afc33f45",
+      "description": "matching birthday for same date",
+      "property": "matchingBirthday",
+      "input": {
+        "birthday1": "2000-01-01",
+        "birthday2": "2000-01-01"
+      },
+      "expected": true
+    },
+    {
+      "uuid": "7193409a-6e16-4bcb-b4cc-9ffe55f79b25",
+      "description": "matching birthday for same year and month but different day",
+      "property": "matchingBirthday",
+      "input": {
+        "birthday1": "2012-05-09",
+        "birthday2": "2012-05-17"
+      },
+      "expected": false
+    },
+    {
+      "uuid": "d04db648-121b-4b72-93e8-d7d2dced4495",
+      "description": "matching birthday for same month and day but different year",
+      "property": "matchingBirthday",
+      "input": {
+        "birthday1": "1999-10-23",
+        "birthday2": "1988-10-23"
+      },
+      "expected": true
+    },
+    {
+      "uuid": "3c8bd0f0-14c6-4d4c-975a-4c636bfdc233",
+      "description": "matching birthday for same year but different month and day",
+      "property": "matchingBirthday",
+      "input": {
+        "birthday1": "2007-12-19",
+        "birthday2": "2007-04-27"
+      },
+      "expected": false
+    },
+    {
+      "uuid": "df5daba6-0879-4480-883c-e855c99cdaa3",
+      "description": "matching birthday for different year month and day",
+      "property": "matchingBirthday",
+      "input": {
+        "birthday1": "1997-08-04",
+        "birthday2": "1963-11-23"
+      },
+      "expected": false
+    },
+    {
+      "uuid": "70b38cea-d234-4697-b146-7d130cd4ee12",
+      "description": "random birthdays return specified number of birthdays",
+      "scenarios": ["random"],
+      "property": "randomBirthdays",
+      "input": {},
+      "expected": "length == groupsize"
+    },
+    {
+      "uuid": "d9d5b7d3-5fea-4752-b9c1-3fcd176d1b03",
+      "description": "random birthdays have fixed year per batch",
+      "scenarios": ["random"],
+      "property": "randomBirthdays",
+      "input": {},
+      "expected": {
+        "years": {
+          "fixed": true
+        }
+      }
+    },
+    {
+      "uuid": "8da69a53-6900-4b63-897d-9f025f149fd2",
+      "description": "random birthdays have random year between batches",
+      "scenarios": ["random"],
+      "property": "randomBirthdays",
+      "input": {},
+      "expected": {
+        "years": {
+          "random": true
+        }
+      }
+    },
+    {
+      "uuid": "d1074327-f68c-4c8a-b0ff-e3730d0f0521",
+      "description": "random birthdays have random months",
+      "scenarios": ["random"],
+      "property": "randomBirthdays",
+      "input": {},
+      "expected": {
+        "months": {
+          "random": true
+        }
+      }
+    },
+    {
+      "uuid": "7df706b3-c3f5-471d-9563-23a4d0577940",
+      "description": "random birthdays have random days",
+      "scenarios": ["random"],
+      "property": "randomBirthdays",
+      "input": {},
+      "expected": {
+        "days": {
+          "random": true
+        }
+      }
+    },
+    {
+      "uuid": "ade37c87-f41d-4929-962a-286b4d1d048a",
+      "description": "has matching birthdays with matching birthday pair",
+      "property": "hasMatchingBirthdays",
+      "input": {
+        "birthdays": ["1970-01-19", "1975-06-03", "2003-01-19"]
+      },
+      "expected": true
+    },
+    {
+      "uuid": "1d155b33-c6e1-46b9-81fa-09123ae378ea",
+      "description": "has matching birthdays without matching birthday pair",
+      "property": "hasMatchingBirthdays",
+      "input": {
+        "birthdays": ["1984-04-05", "2000-09-17", "1966-10-12"]
+      },
+      "expected": false
+    },
+    {
+      "uuid": "89a462a4-4265-4912-9506-fb027913f221",
+      "description": "probability for matching birthday for one person",
+      "scenarios": ["random"],
+      "property": "probabilityForMatchingBirthdays",
+      "input": {
+        "groupSize": 1
+      },
+      "expected": 0.0
+    },
+    {
+      "uuid": "ec31c787-0ebb-4548-970c-5dcb4eadfb5f",
+      "description": "probability for matching birthday for ten people",
+      "scenarios": ["random"],
+      "property": "probabilityForMatchingBirthdays",
+      "input": {
+        "groupSize": 10
+      },
+      "expected": 11.7
+    },
+    {
+      "uuid": "b548afac-a451-46a3-9bb0-cb1f60c48e2f",
+      "description": "probability for matching birthday for twenty-three people",
+      "scenarios": ["random"],
+      "property": "probabilityForMatchingBirthdays",
+      "input": {
+        "groupSize": 23
+      },
+      "expected": 50.7
+    },
+    {
+      "uuid": "e43e6b9d-d77b-4f6c-a960-0fc0129a0bc5",
+      "description": "probability for matching birthday for seventy people",
+      "scenarios": ["random"],
+      "property": "probabilityForMatchingBirthdays",
+      "input": {
+        "groupSize": 70
+      },
+      "expected": 99.9
+    }
+  ]
+}

exercises/baffling-birthdays/instructions.md

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

exercises/baffling-birthdays/introduction.md

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

exercises/baffling-birthdays/metadata.toml

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+title = "Baffling Birthdays"
+blurb = "Verify the Birthday Paradox's probabilities."
+source = "Erik Schierboom"
+source_url = "https://github.com/exercism/problem-specifications/pull/2539"