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Solution written in Go for challenge 2012-10-12 on ProgrammingPraxis.com
// The MIT License (MIT)
// Copyright (c) 2012 Christian Siegert
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
// Exercise:
// In the study of probability, the Birthday Paradox states that in a group of
// 23 people, there is a 50% chance that two will have the same birthday; in a
// group of 57 people, the odds rise to 99%. Your task is to simulate the
// birthday paradox over many trials and verify the odds.
// http://programmingpraxis.com/2012/10/12/birthday-paradox/
package main
import (
"fmt"
"math/rand"
)
func main() {
fmt.Printf("Chance of same birthday in group with 23 people: %.0f%%\n", getChanceOfSameBirthdayInGroup(23)*100)
fmt.Printf("Chance of same birthday in group with 57 people: %.0f%%\n", getChanceOfSameBirthdayInGroup(57)*100)
}
func getChanceOfSameBirthdayInGroup(groupSize uint) float32 {
n := 10000
numberOfSameBirthdays := 0
for i := 0; i < n; i++ {
if isSameBirthdayInGroup(groupSize) {
numberOfSameBirthdays++
}
}
return float32(numberOfSameBirthdays) / float32(n)
}
func isSameBirthdayInGroup(groupSize uint) bool {
birthdays := make(map[int]uint8)
for i := uint(0); i < groupSize; i++ {
birthday := rand.Intn(365)
birthdays[birthday]++
if birthdays[birthday] == 2 {
return true
}
}
return false
}
@ChristianSiegert

Console output:

$ go run challenge-2012-10-12.go
Chance of same birthday in group with 23 people: 50%
Chance of same birthday in group with 57 people: 99%
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