A scala solution to the binary watch problem: https://leetcode.com/problems/binary-watch/

BinaryWatch.scala

object BinaryWatch extends App {

  def hasBitCount(count: Int)(binTime: Int): Boolean = Integer.bitCount(binTime) == count

  case class Time(hour: Int, minute: Int)

  def parseTime(time: Int): Option[Time] = {
    val hour = time >> 6
    val minute = time & ((1 << 6) - 1)

    if (hour < 12 && minute < 60)
      Some(Time(hour, minute))
    else
      None
  }

  def formatTime(time: Time): String = f"${time.hour}:${time.minute}%02d"

  // main function, as required by the problem
  def readBinaryWatch(num: Int): List[String] = {
    val maxBitCount = 10
    val maxNum = (1 << maxBitCount) - 1

    Stream.range(0, maxNum)
      .filter(hasBitCount(num))
      .flatMap(parseTime)
      .map(formatTime)
      .toList
  }

  for (i <- 0 to 10) {
    val values = readBinaryWatch(i)
    println(s"Watch faces with $i bits: $values")
  }
}