Range and Sequence Generators

@main def run(): Unit =
  // Ranges
  val r1 = 1 to 10          // inclusive
  val r2 = 1 until 10       // exclusive
  val r3 = 1 to 20 by 3     // step
  val r4 = 10 to 1 by -1    // descending
  val r5 = 0.0 to 1.0 by 0.1  // double range

  println(s"1 to 10: ${r1.toList}")
  println(s"1 until 10: ${r2.toList}")
  println(s"By 3: ${r3.toList}")
  println(s"Descending: ${r4.toList}")
  println(f"Double: ${r5.toList.map(d => f"$d%.1f")}")

  // List generators
  val filled = List.fill(5)("x")
  val tabulated = List.tabulate(5)(n => n * n)
  val iterated = List.iterate(1, 10)(_ * 2)  // powers of 2

  println(s"Fill: $filled")
  println(s"Tabulate: $tabulated")
  println(s"Iterate: $iterated")

  // Vector generators
  val matrix = Vector.tabulate(3, 4)((r, c) => r * 4 + c + 1)
  matrix.foreach(row => println(s"  ${row.mkString("\t")}"))

  // Array generators
  val zeros = Array.fill(5)(0)
  val indices = Array.tabulate(5)(identity)
  println(s"Zeros: ${zeros.mkString(", ")}")
  println(s"Indices: ${indices.mkString(", ")}")

  // Unfold (generate from state)
  val collatz = List.unfold(27) { n =>
    if n == 1 then None
    else if n % 2 == 0 then Some((n, n / 2))
    else Some((n, 3 * n + 1))
  }
  println(s"Collatz(27): $collatz")

  // Generate with condition
  val fibs = List.unfold((0, 1)) { (a, b) =>
    if a > 100 then None
    else Some((a, (b, a + b)))
  }
  println(s"Fibs < 100: $fibs")

  // Combination generators
  val combos = for
    suit <- List("♠", "♥", "♦", "♣")
    rank <- List("A", "K", "Q", "J") ++ (2 to 10).map(_.toString)
  yield s"$rank$suit"
  println(s"Deck size: ${combos.size}")
  println(s"First 8: ${combos.take(8).mkString(", ")}")

  // Repeated application
  val doubling = Iterator.iterate(1)(_ * 2).take(10).toList
  println(s"Doubling: $doubling")

  // Zip with index
  val fruits = List("apple", "banana", "cherry")
  val numbered = fruits.zipWithIndex.map((f, i) => s"${i + 1}. $f")
  println(numbered.mkString(", "))