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Add baffling-birthdays exercise
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‎exercises/baffling-birthdays/canonical-data.json

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

‎exercises/baffling-birthdays/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/baffling-birthdays/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/baffling-birthdays/metadata.toml

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title = "Baffling Birthdays"
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blurb = "Verify the Birthday Problem's probabilities."
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source = "Erik Schierboom"

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