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 {p => // p[i] is the column of the queen on ith row (must be a permutation of 0 until n)
  val i = p.zipWithIndex.toSet
  i.map{case (c, d) => c + d}.size == n && i.map{case (c, d) => c - d}.size == n  // No 2 queens can have same col + diag or col - diag
}

for {
  (solution, num) <- nQueens(8).zipWithIndex
  _ = println(s"Solution #${num + 1}:")
  col <- solution
  row = solution.indices.map(i => if (i == col) 'Q' else '-')
} println(row.mkString)