public ArrayList<BookNode> getSelectedNodes(){
		ArrayList<BookNode> selectedNodes = new ArrayList<>();
		for(int i = 0;i < cells.length;i++){
			for(int j = 0;j < cells[i].length;j++){
				GridCell current = cells[i][j];
				selectedNodes.addAll(current.getSelectedNodes());
			}
		}
		return selectedNodes;
	}