e-queens (force brute)

import scala.annotation.tailrec

case class Pos(x: Int, y: Int)

object Queen {
  def isSafe(a: Pos, b: Pos): Boolean = {
    a.x != b.x && a.y != b.y && Math.abs(a.x - b.x) != Math.abs(a.y - b.y)
  }

  def isSafe(a: Pos, queens: List[Pos]): Boolean = queens match {
    case Nil => true
    case _ => queens.forall(isSafe(a, _))
  }

  @tailrec
  def findListSafe(listQueens: List[Pos]): Boolean = {
    listQueens match {
      case Nil => true
      case x :: xs => isSafe(x, xs) && findListSafe(xs)
    }
  }

}

(for (x <- List(Nil); y <- 0 to 5) yield (x, y)).foreach(println)

def calculateQueens(y: Int, n: Int): Vector[List[Pos]] = {

  if (y < 0)
    Vector(Nil)
  else
    for (
      queens <- calculateQueens(y - 1, n);
      x <- 0 to n if (Queen.isSafe(Pos(x, y), queens)))
    yield Pos(x, y) +: queens

}

val size = 12

val combinations = calculateQueens(size, size)

def printBoard(size: Int, listQueens: List[Pos]) = {
  for (y <- 0 to size) {
     for (x <- 0 to size) {

        if (listQueens.contains(Pos(x, y)))
          print("Q ")
        else
          print("* ")
     }

     println()
  }
}

printBoard(size, combinations.collectFirst { case i => i }.head)

/*

Q * * * * * * * * * * * * 
* * Q * * * * * * * * * * 
* * * * Q * * * * * * * * 
* Q * * * * * * * * * * * 
* * * * * * * * Q * * * * 
* * * * * * * * * * * Q * 
* * * * * * * * * Q * * * 
* * * * * * * * * * * * Q 
* * * Q * * * * * * * * * 
* * * * * Q * * * * * * * 
* * * * * * * Q * * * * * 
* * * * * * * * * * Q * * 
* * * * * * Q * * * * * * 

*/