Scala Knight’s Tour

Scala program showing Knight’s Tour iterative algorithm using ASCII chars for demonstration
Main.scala

package net.theflyingkeyboard.knightour

// ? 2020 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
object Main extends App {
  val size = 8
  var initialBoard: List[List[Char]] = List.tabulate(size, size)((_, _) => Board.EMPTY)
  initialBoard = initialBoard.updated(0, initialBoard.head.updated(0, Board.KNIGHT))

  var knightPosition = BoardPoint(0, 0)
  var board = Board(initialBoard, knightPosition)
  var possibleMoves = board.possibleMoves(knightPosition)

  println(board)
  println()

  while (possibleMoves.length > 0) {
    val sortedMoves = possibleMoves.map(move => (move, board.possibleMoves(move)))
      .sortBy(moveMoves => moveMoves._2.length)

    knightPosition = sortedMoves(0)._1
    board = board.placeKnight(knightPosition)
    possibleMoves = board.possibleMoves(knightPosition)

    println(board)
    println()
  }
}

BoardPoint.scala

package net.theflyingkeyboard.knightour

// ? 2020 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
case class BoardPoint(x: Int, y: Int)

Board.scala

package net.theflyingkeyboard.knightour

// ? 2020 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
class Board(board: List[List[Char]], knightPosition: BoardPoint) {
  def possibleMoves(nextPosition: BoardPoint): Array[BoardPoint] = {
    Board.KNIGHT_MOVES.map(bP => BoardPoint(bP.x + nextPosition.x, bP.y + nextPosition.y))
      .filter(bP => bP.x < board.head.length && bP.x >= 0)
      .filter(bP => bP.y < board.length && bP.y >= 0)
      .filter(bP => board(bP.y)(bP.x) == Board.EMPTY)
  }

  def placeKnight(position: BoardPoint): Board = {
    def updateBoard(boardToUpdate: List[List[Char]], point: BoardPoint, value: Char): List[List[Char]] = {
      boardToUpdate.updated(point.y, boardToUpdate(point.y).updated(point.x, value))
    }

    val replacedKnight = updateBoard(board, knightPosition, Board.VISITED)
    val newKnightPlaced = updateBoard(replacedKnight, position, Board.KNIGHT)

    Board(newKnightPlaced, position)
  }

  override def toString: String = {
    board.map(row => row.mkString(""))
    .mkString("\n")
  }
}

object Board {
  val EMPTY = '.'
  val VISITED = 'X'
  val KNIGHT = 'K'

  private val KNIGHT_MOVES: Array[BoardPoint] = Array(BoardPoint(2, 1), BoardPoint(1, 2), BoardPoint(-1, 2),
    BoardPoint(-2, 1), BoardPoint(-2, -1), BoardPoint(-1, -2), BoardPoint(1, -2), BoardPoint(2, -1))

  def apply(board: List[List[Char]], knightPosition: BoardPoint): Board = new Board(board, knightPosition)
}