题解 | 【模板】序列操作

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int q = in.nextInt();
        List<Integer> list = new ArrayList<>();
        while (q-- > 0) {
            int n = in.nextInt();
            if(n==1){
                int x = in.nextInt();
                list.add(x);
            }
            else if (n == 2) {
                int len = list.size();
                if(len>0)
                list.remove(len - 1);
            }
            else if(n==3){
                int i = in.nextInt();
                System.out.println(list.get(i));
            }
            else if (n == 4) {
                int i = in.nextInt();
                int x = in.nextInt();
                list.add(i+1, x);
            }
            else if (n == 5) {
                Collections.sort(list);
            }
            else if (n == 6) {
                Collections.sort(list, Comparator.reverseOrder());
                // list.sort(Comparator.reverseOrder());
            }
            else if (n == 7) {
                System.out.println(list.size());
            }
            else if (n == 8) {
                for (int i : list) {
                    System.out.printf("%d ", i);
                }
                System.out.println();
            }
        }
    }
}