题解 | #【模板】栈#

public static void main(String[] args) {
    List<Integer> list=new LinkedList<>();
    try(BufferedReader br=new BufferedReader(new InputStreamReader(System.in))){
        String str=br.readLine();
        int r=Integer.valueOf(str);
        while (r != 0){
            str=br.readLine();
            if(str.startsWith("push")){
                list.add(0,Integer.valueOf(str.split(" ")[1]));
            }else if(str.equals("pop")){
                if(list.size()==0){
                    System.out.println("error");
                }else{
                    System.out.println(list.get(0));
                    list.remove(0);
                }
            }else if(str.equals("top")) {
                if (list.size() == 0) {
                    System.out.println("error");
                } else {
                    System.out.println(list.get(0));
                }
            }
            r--;
        }
     }catch (Exception e){e.printStackTrace();}
}