题解 | 【模板】序列操作

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int numOperation = Integer.parseInt(in.nextLine());
        ArrayList<Integer> list = new ArrayList<Integer>();

        for(int i = 0; i < numOperation; i++) {
            String input = in.nextLine();
            List<Integer> operation = Arrays.stream(input.split(" ")).map(Integer::parseInt).collect(Collectors.toList());
            switch(operation.get(0)) {
                case 1: 
                    list.add(operation.get(1));
                    break;
                case 2:
                    list.remove(list.size() - 1);
                    break;
                case 3:
                    System.out.println(list.get(operation.get(1)));
                    break;
                case 4:
                    list.add(operation.get(1) + 1, operation.get(2));// 向第i个数与第i+1个数中间添加是添加到i+1的位置
                    break;
                case 5:
                    list.sort((a,b) -> a - b);
                    break;
                case 6:
                    list.sort((a,b) -> b - a);
                    break;
                case 7:
                    System.out.println(list.size());
                    break;
                case 8:
                    System.out.println(list.stream().map(String::valueOf).collect(Collectors.joining(" ")));
                    break;
            }

        }
    }
}