O(n!) solution to the n-Queen puzzle (https://en.wikipedia.org/wiki/Eight_queens_puzzle)

NQueen.scala

def nQueens(n: Int) = (0 until n).permutations filter {col =>   // col[r] = column of queen on r-th row
  val p = col.zipWithIndex.toSet            // col[] must be a permutation of (0 until n) because of rook attacks 
  p.map{case (c, d) => c + d}.size == n &&  // No 2 queens can have same col + diag because of left-bishop attacks
  p.map{case (c, d) => c - d}.size == n     // No 2 queens can have same col - diag because of right-bishop attacks
}
/*************************************** [Printing code below] *************************************************/
for ((solution, num) <- nQueens(8).zipWithIndex) {
  println(s"Solution #${num + 1}:")
  solution foreach {col =>
    val row = solution.indices.map(i => if (i == col) 'Q' else '-')
    println(row.mkString)
  }
}
// Feel free to run this code on http://scalafiddle.net