Scala - 用随机数填充 Seq，不重复且始终具有相同大小

Question

I would like to create a Seq of Ints with size always equal to 3. If a number is from range 0 to 10 then I want to return always a Seq of 3 same numbers. If number is from other range, then I want to return a Seq of 3 random numbers, but without duplicates. I created a code for this:

object Simulator {
  def toSeq(value: => Int): Seq[Int] = Seq.fill(3)(value)

  def shuffle(): Seq[Int] = {
    val seq = 0 to 100
    val number = Random.nextInt(seq.length)
    number match {
      case _ if 0 to 10 contains number => toSeq(number)
      case _ => toSeq(Random.nextInt(seq.count(_ != number)))
    }
  }
}

But in the second case I can randomize 1, 2 or 3 same numbers and then size of my Seq is 1 or 2 (after remove duplicates). How could I change this code to similar but always return Seq with length 3?

Answer 1

def shuffle(): Seq[Int] = {
  val nums = util.Random.shuffle(Seq.tabulate(101)(identity))
  if (nums.head < 11) Seq.fill(3)(nums.head)
  else nums.take(3)
}

Notice: if the 1st number is outside the 0-to-10 range, the 2nd and/or 3rd numbers are still only restricted to the 0-to-100 range.

Answer 2

Here is a recursive approach:

def threeRands(n : Int, acc : Seq[Int] = Seq()) : Seq[Int] = {
  val num = Random.nextInt(n)
  if(n <= 0) Seq.fill(3)(-1)
  else if(n > 0  && n < 11) {
    Seq.fill(3)(num)
  } else {
    if(acc.size==3) acc
    else if(acc.contains(num)) threeRands(n, acc)
    else threeRands(n, acc :+ num)
  }
}

threeRands(4) //res0: Seq[Int] = List(1, 1, 1)
threeRands(13) //res1: Seq[Int] = List(9, 3, 4)
threeRands(1000) //res2: res2: Seq[Int] = List(799, 227, 668)

This can be optimized more by extracting the < 11 case or using Set instead of Seq . Note that if the size of sequence was much larger than 3, this could take a long time so it might be better to add another variable to keep track of number of trials to get the sequence with the required length.