func Q(_ n:Int,_ x:Int=0,_ a:[Int]=[])->[[Int]]{
x==n ?[a]:(0..<n).filter{(y:Int)in !a.contains(y)&&(0..<x).filter{x-$0==abs(y-a[$0])}.isEmpty}.flatMap{Q(n,x+1,a+[$0])}
}
--
FROM 219.79.94.*