Hanoi.scala

import scala.collection.mutable.Stack

class Peg(val disks: Stack[Int], val name: String)

def solveHanoi_1(n: Int): Unit = {
  val A = Peg(Stack[Int](1 to n: _*), "A")
  val B = Peg(Stack[Int](), "B")
  val C = Peg(Stack[Int](), "C")

  val evenSeq = Seq((A, B), (A, C), (B, C))
  val oddSeq = Seq((A, C), (A, B), (B, C))

  def solve(moves: Seq[(Peg, Peg)]): Unit = {
    var counter = 0;
    
    while (C.disks.size != n) {
      val idx = counter % 3;
      val pegs = orderPegs(moves(idx))
      move(pegs)
      counter = counter + 1;
    }
  }

  def orderPegs(pegPair: (Peg, Peg)): (Peg, Peg) = {
    val peg1 = pegPair._1
    val peg2 = pegPair._2

    if (peg1.disks.isEmpty || (!peg2.disks.isEmpty && (peg1.disks.head > peg2.disks.head))) {
      (peg2, peg1)
    } else {
      pegPair
    }
  }

  def move(pegs: (Peg, Peg)): Unit = {
    val from = pegs._1
    val to = pegs._2

    val disk = from.disks.pop
    println(s"Moving a disk of size $disk from ${from.name} to ${to.name}")
    to.disks.push(disk)
  }

  if (n % 2 == 0) {
    solve(evenSeq)
  } else {
    solve(oddSeq)
  }
}

solveHanoi_1(3)

def solveHanoi(size: Int, from: String, to: String, extra: String): Unit = {
  if(size != 0) {
    solveHanoi(size - 1, from, extra, to);
    println(s"Moving peg of size $size from $from to $to")
    solveHanoi(size - 1, extra, to, from)
  }
}

solveHanoi(3, "A", "B", "C")