题解 | 【模板】序列操作

序列在Java中其实就是集合，这道题其实是考察我们对集合的理解，大多数选项都是集合的自带的方法，但是那个在i和i+1之间插入的，我一下子找不到对应方法只能手写了

import java.util.ArrayList;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<Integer> list = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        int q = scanner.nextInt();
        for (int i = 0; i < q; i++) {
            int n = scanner.nextInt();
            if (n == 1) {
                int x = scanner.nextInt();
                list.add(x);
            } else if (n == 2) {
                list.remove(list.size() - 1);
            } else if (n == 3) {
                int j = scanner.nextInt();
                System.out.println(list.get(j));
            } else if (n == 4) {
                int j = scanner.nextInt();
                int x = scanner.nextInt();
                int a[] = new int[list.size() + 1];
                a[j + 1] = x;
                ArrayList<Integer> list1 = new ArrayList<>();
                for (int k = 0; k < a.length; k++) {
                    if (k == j + 1) {
                        list1.add(a[k]);
                        continue;
                    }
                    if (k > j + 1) {
                        a[k] = list.get(k - 1);
                    } else {
                        a[k] = list.get(k);
                    }
                    list1.add(a[k]);

                }
                list = new ArrayList<>(list1);
            } else if (n == 5) {
                list.sort((s1, s2)->s1 - s2);
            } else if (n == 6) {
                list.sort((s1, s2)->s2 - s1);
            } else if (n == 7) {
                System.out.println(list.size());
            } else if (n == 8) {
                for (Integer j : list) {
                    System.out.print(j + " ");
                }
                System.out.println();
            }
        }


    }

}