public static void main(String[] args){
        List<String[]> list = new N_Queens().solveNQueens(4);
        String[] board;
        for(int i = 0; i< list.size();i++){
            board = list.get(i);
            for(int j = 0 ; j < board.length;j++)
                System.out.println(board[j].toString());

            System.out.println("*****************");
        }

    }