Cheryl's birthday: Difference between revisions

=={{header|Scala}}==

{{trans|D}}

<lang scala>import java.time.format.DateTimeFormatter

import java.time.{LocalDate, Month}

object Cheryl {

def main(args: Array[String]): Unit = {

val choices = List(

LocalDate.of(2019, Month.MAY, 15),

LocalDate.of(2019, Month.MAY, 16),

LocalDate.of(2019, Month.MAY, 19),

LocalDate.of(2019, Month.JUNE, 17),

LocalDate.of(2019, Month.JUNE, 18),

LocalDate.of(2019, Month.JULY, 14),

LocalDate.of(2019, Month.JULY, 16),

LocalDate.of(2019, Month.AUGUST, 14),

LocalDate.of(2019, Month.AUGUST, 15),

LocalDate.of(2019, Month.AUGUST, 17)

)

// The month cannot have a unique day because Albert knows the month, and knows that Bernard does not know the answer

val uniqueMonths = choices.groupBy(_.getDayOfMonth)

.filter(a => a._2.length == 1)

.flatMap(a => a._2)

.map(a => a.getMonth)

val filter1 = choices.filterNot(a => uniqueMonths.exists(b => a.getMonth == b))

// Bernard now knows the answer, so the day must be unique within the remaining choices

val uniqueDays = filter1.groupBy(_.getDayOfMonth)

.filter(a => a._2.length == 1)

.flatMap(a => a._2)

.map(a => a.getDayOfMonth)

val filter2 = filter1.filter(a => uniqueDays.exists(b => a.getDayOfMonth == b))

// Albert knows the answer too, so the month must be unique within the remaining choices

val birthDay = filter2.groupBy(_.getMonth)

.filter(a => a._2.length == 1)

.flatMap(a => a._2)

.head

// print the result

printf(birthDay.format(DateTimeFormatter.ofPattern("MMMM dd")))

}

}</lang>

{{out}}

<pre>July 16</pre>