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Add baffling-birthdays
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‎config.json‎

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"prerequisites": [],
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"difficulty": 5
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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": "07082d28-7689-4c2b-a613-3087031a4b39",
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"practices": [],
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"prerequisites": [],
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"difficulty": 6
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},
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{
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"slug": "knapsack",
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"name": "Knapsack",

‎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/.meta/config.json‎

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{
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"authors": [
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"keiravillekode"
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],
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"files": {
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"solution": [
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"baffling_birthdays.s"
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],
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"test": [
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"baffling_birthdays_test.c"
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],
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"example": [
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".meta/example.s"
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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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}

‎exercises/practice/baffling-birthdays/.meta/example.s‎

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.text
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.globl shared_birthday
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.globl estimate
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/* extern bool shared_birthday(const char **birthdates); */
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shared_birthday:
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stp xzr, xzr, [sp, #-64]! /* 32 halfwords on stack */
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stp xzr, xzr, [sp, #16]
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stp xzr, xzr, [sp, #32]
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stp xzr, xzr, [sp, #48]
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mov x2, x0
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mov x0, xzr
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mov w1, #1
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mov w10, #10
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mov w15, 528 /* 11 * '0' */
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.birthdate:
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ldr x9, [x2], #8
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cbz x9, .return
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ldrb w11, [x9, #8]
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ldrb w13, [x9, #9]
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madd w13, w10, w11, w13
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sub w13, w13, w15 /* day 1..31 */
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lsl w13, w13, #1
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ldrb w11, [x9, #5]
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ldrb w12, [x9, #6]
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madd w12, w10, w11, w12
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sub w12, w12, w15 /* month 1..12 */
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lsl w12, w1, w12 /* 1 << month */
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ldrh w11, [sp, x13]
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orr w12, w11, w12
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strh w12, [sp, x13]
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cmp w11, w12
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bne .birthdate
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mov x0, #1
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.return:
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add sp, sp, #64
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ret
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/* extern double estimate(int group_size); */
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estimate:
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mov w9, #1
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mov w10, #100
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mov w11, #365
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scvtf d0, w9 /* probability of no shared birthday */
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scvtf d1, w9
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scvtf d2, w11 /* descending numerator */
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scvtf d3, w11 /* constant denominator */
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scvtf d4, w10
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cbz w0, .complement
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.multiply:
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fmul d0, d0, d2 /* multiply by 365, 364, 363, ... */
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fdiv d0, d0, d3 /* divide by 365 */
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fsub d2, d2, d1
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add w0, w0, #-1 /* number of remaining birthdates */
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cbnz w0, .multiply
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.complement:
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fsub d0, d1, d0 /* probability of shared birthday */
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fmul d0, d0, d4 /* convert to percentage */
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ret

‎exercises/practice/baffling-birthdays/.meta/tests.toml‎

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[716dcc2b-8fe4-4fc9-8c48-cbe70d8e6b67]
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description = "shared birthday -> one birthdate"
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[f7b3eb26-bcfc-4c1e-a2de-af07afc33f45]
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description = "shared birthday -> two birthdates with same year, month, and day"
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[7193409a-6e16-4bcb-b4cc-9ffe55f79b25]
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description = "shared birthday -> two birthdates with same year and month, but different day"
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[d04db648-121b-4b72-93e8-d7d2dced4495]
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description = "shared birthday -> two birthdates with same month and day, but different year"
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[3c8bd0f0-14c6-4d4c-975a-4c636bfdc233]
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description = "shared birthday -> two birthdates with same year, but different month and day"
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[df5daba6-0879-4480-883c-e855c99cdaa3]
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description = "shared birthday -> two birthdates with different year, month, and day"
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[0c17b220-cbb9-4bd7-872f-373044c7b406]
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description = "shared birthday -> multiple birthdates without shared birthday"
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[966d6b0b-5c0a-4b8c-bc2d-64939ada49f8]
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description = "shared birthday -> multiple birthdates with one shared birthday"
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[b7937d28-403b-4500-acce-4d9fe3a9620d]
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description = "shared birthday -> multiple birthdates with more than one shared birthday"
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[70b38cea-d234-4697-b146-7d130cd4ee12]
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description = "random birthdates -> generate requested number of birthdates"
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include = false
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[d9d5b7d3-5fea-4752-b9c1-3fcd176d1b03]
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description = "random birthdates -> years are not leap years"
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include = false
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[d1074327-f68c-4c8a-b0ff-e3730d0f0521]
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description = "random birthdates -> months are random"
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include = false
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[7df706b3-c3f5-471d-9563-23a4d0577940]
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description = "random birthdates -> days are random"
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include = false
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[89a462a4-4265-4912-9506-fb027913f221]
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description = "estimated probability of at least one shared birthday -> for one person"
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[ec31c787-0ebb-4548-970c-5dcb4eadfb5f]
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description = "estimated probability of at least one shared birthday -> among ten people"
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[b548afac-a451-46a3-9bb0-cb1f60c48e2f]
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description = "estimated probability of at least one shared birthday -> among twenty-three people"
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[e43e6b9d-d77b-4f6c-a960-0fc0129a0bc5]
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description = "estimated probability of at least one shared birthday -> among seventy people"

‎exercises/practice/baffling-birthdays/Makefile‎

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ifeq ($(origin AS),default)
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AS = aarch64-linux-gnu-as
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endif
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ifeq ($(origin CC),default)
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CC = aarch64-linux-gnu-gcc
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endif
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CFLAGS ?= -g -Wall -Wextra -pedantic -Werror
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LDFLAGS =
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ALL_LDFLAGS = -pie -Wl,--fatal-warnings
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ALL_CFLAGS = -std=c99 -fPIE $(CFLAGS)
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ALL_LDFLAGS += $(LDFLAGS)
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C_OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
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AS_OBJS = $(patsubst %.s,%.o,$(wildcard *.s))
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ALL_OBJS = $(filter-out example.o,$(C_OBJS) $(AS_OBJS) vendor/unity.o)
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CC_CMD = $(CC) $(ALL_CFLAGS) -c -o $@ $<
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PLATFORM = $(shell uname -m)
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ifeq ($(PLATFORM),aarch64)
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MAYBE_QEMU =
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else
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MAYBE_QEMU = qemu-aarch64 -L /usr/aarch64-linux-gnu
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endif
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all: tests
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@$(MAYBE_QEMU) ./$<
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tests: $(ALL_OBJS)
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@$(CC) $(ALL_CFLAGS) $(ALL_LDFLAGS) -o $@ $(ALL_OBJS)
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%.o: %.s
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@$(AS) -o $@ $<
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%.o: %.c
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@$(CC_CMD)
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vendor/unity.o: vendor/unity.c vendor/unity.h vendor/unity_internals.h
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@$(CC_CMD)
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clean:
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@rm -f *.o vendor/*.o tests
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.PHONY: all clean

‎exercises/practice/baffling-birthdays/baffling_birthdays.s‎

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.text
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.globl shared_birthday
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.globl estimate
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shared_birthday:
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ret
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estimate:
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ret

‎exercises/practice/baffling-birthdays/baffling_birthdays_test.c‎

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#include "vendor/unity.h"
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#include <stddef.h>
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#include <stdbool.h>
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extern bool shared_birthday(const char **birthdates);
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// estimated probability of shared birthday
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extern double estimate(int group_size);
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void setUp(void) {
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}
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void tearDown(void) {
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}
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void test_one_birthdate(void) {
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const char *birthdates[] = {"2000-01-01", NULL};
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TEST_ASSERT_FALSE(shared_birthday(birthdates));
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}
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void test_two_birthdates_with_same_year_month_and_day(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"2000-01-01", "2000-01-01", NULL};
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TEST_ASSERT_TRUE(shared_birthday(birthdates));
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}
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void test_two_birthdates_with_same_year_and_month_but_different_day(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"2012-05-09", "2012-05-17", NULL};
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TEST_ASSERT_FALSE(shared_birthday(birthdates));
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}
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void test_two_birthdates_with_same_month_and_day_but_different_year(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"1999-10-23", "1988-10-23", NULL};
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TEST_ASSERT_TRUE(shared_birthday(birthdates));
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}
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void test_two_birthdates_with_same_year_but_different_month_and_day(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"2007-12-19", "2007-04-27", NULL};
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TEST_ASSERT_FALSE(shared_birthday(birthdates));
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}
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void test_two_birthdates_with_different_year_month_and_day(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"1997-08-04", "1963-11-23", NULL};
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TEST_ASSERT_FALSE(shared_birthday(birthdates));
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}
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void test_multiple_birthdates_without_shared_birthday(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"1966-07-29", "1977-02-12", "2001-12-25", "1980-11-10", NULL};
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TEST_ASSERT_FALSE(shared_birthday(birthdates));
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}
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void test_multiple_birthdates_with_one_shared_birthday(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"1966-07-29", "1977-02-12", "2001-07-29", "1980-11-10", NULL};
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TEST_ASSERT_TRUE(shared_birthday(birthdates));
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}
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void test_multiple_birthdates_with_more_than_one_shared_birthday(void) {
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TEST_IGNORE();
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const char *birthdates[] = {"1966-07-29", "1977-02-12", "2001-12-25", "1980-07-29", "2019-02-12", NULL};
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TEST_ASSERT_TRUE(shared_birthday(birthdates));
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}
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void test_for_one_person(void) {
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TEST_IGNORE();
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TEST_ASSERT_FLOAT_WITHIN(0.05, 0.0, estimate(1));
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}
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void test_among_ten_people(void) {
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TEST_IGNORE();
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TEST_ASSERT_FLOAT_WITHIN(0.05, 11.694818, estimate(10));
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}
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void test_among_twentythree_people(void) {
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TEST_IGNORE();
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TEST_ASSERT_FLOAT_WITHIN(0.05, 50.729723, estimate(23));
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}
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void test_among_seventy_people(void) {
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TEST_IGNORE();
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TEST_ASSERT_FLOAT_WITHIN(0.05, 99.915958, estimate(70));
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}
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int main(void) {
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UNITY_BEGIN();
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RUN_TEST(test_one_birthdate);
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RUN_TEST(test_two_birthdates_with_same_year_month_and_day);
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RUN_TEST(test_two_birthdates_with_same_year_and_month_but_different_day);
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RUN_TEST(test_two_birthdates_with_same_month_and_day_but_different_year);
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RUN_TEST(test_two_birthdates_with_same_year_but_different_month_and_day);
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RUN_TEST(test_two_birthdates_with_different_year_month_and_day);
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RUN_TEST(test_multiple_birthdates_without_shared_birthday);
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RUN_TEST(test_multiple_birthdates_with_one_shared_birthday);
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RUN_TEST(test_multiple_birthdates_with_more_than_one_shared_birthday);
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RUN_TEST(test_for_one_person);
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RUN_TEST(test_among_ten_people);
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RUN_TEST(test_among_twentythree_people);
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RUN_TEST(test_among_seventy_people);
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return UNITY_END();
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}

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