Using swi prolog code a tail-recursive solution for the nqueens problem.

The nqueens problem is placing N amount of queens on an NxN chess board so that none of them are attacking each other.

The position of the queens should be represented as a list where the index of the list is the column and the integer is the row. i.e. [6,7,3,2,8]. A queen is found on the 6th row of the first column.

Do not use cut (!) or constraint logic libraries please. Not quite there in my learning process.

Example run

?- queens(8, Qs).

Qs = [4, 2, 7, 3, 6, 8, 5, 1];

Qs = [5, 2, 4, 7, 3, 8, 6, 1];

....