Sequentially take from shuffled names

import scala.util.Random

class Robot {

  var name = genName()

  def reset() = name = genName()

  private def genName(): String = Robot.names.next()
}

object Robot {
  val names: Iterator[String] = {
    val seqNames =
      for {
        ltr1 <- ('A' to 'Z')
        ltr2 <- ('A' to 'Z')
        num <- (0 to 999)
      } yield {
        f"$ltr1%c$ltr2%c$num%03d"
      }
    Random.shuffle(seqNames).to(LazyList).iterator
  }
}

This approach uses a for comprehension for generating the two letters and number in sequence. It yields a string, using an f interpolator to format leading zeroes for the number as needed for a three-digit representation.

The names are generated into an IndexedSeq which is then shuffle()ed and collected into a LazyList, which is then chained to an Iterator. The Iterator is what is returned from the names value.

Although names keeps returning a different value every time it is called, it is an immutable val because it is not reassigned.

The shuffled approach can finish all the tests, including generating all 676,000 unique names, in about one-and-a-half seconds.