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Discussion on: Daily Challenge #199 - List of All Rationals

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Avalander •

Scala

This was really fun. I want to refine the algorithm to not need to carry each generated level and keep track of where I am, but I didn't have time to fix it right now.

case class Rational(n: Int, d: Int) {
  override def toString (): String = s"$n/$d"
}

def nextLevel (s: LazyList[Rational]): LazyList[Rational] =
  s flatMap {
    case Rational(n, d) => LazyList(
      Rational(n, n + d),
      Rational(n + d, d)
    )
  }

def rationals (from: LazyList[Rational] = LazyList(Rational(1, 1)), pos: Int = 0): LazyList[Rational] = {
  if (pos >= from.size) rationals (nextLevel(from))
  else from(pos) #:: rationals (from, pos + 1)
}