N, queens := 4, queensN(N);
println(queens.len()," solution(s):");
foreach s in (queens){
   println(s,":");
   b = (b := List.createLong(N,"-")).apply(b.copy); // NxN array
   s.apply2('wrap([(r,c)]){ b[r - 1][c - 1] = "Q" });
   b.apply("concat","").concat("\n").println();
}