题解 | 【模板】多重集合操作

import java.util.*;

public class Main {
    public static TreeMap<Integer,Integer> set = new TreeMap<>();
    //TreeMap自动排序
    public static int len = 0;
    public static void insertValue(int x) {
        // TODO: 实现插入逻辑
        set.put(x,set.getOrDefault(x,0)+1);
        //getOrDefault和get区别在于，x不存在get返回null,前者返回指定值 这里指定为0
        len++;
    }

    public static void eraseValue(int x) {
        // TODO: 实现删除逻辑
        if(set.containsKey(x)){
            int count = set.get(x);
            if(count==1){
                set.remove(x);
            }
            else{
                set.put(x,count-1);
            }
            len--;
        }
    }

    public static int xCount(int x) {
        return set.getOrDefault(x,0);
    }

    public static int sizeOfSet() {
        // TODO: 返回集合大小
        return len;
    }

    public static int getPre(int x) {
        // TODO: 实现找前驱
        Integer pre = set.lowerKey(x);
        return pre==null?-1:pre;
    }

    public static int getBack(int x) {
        // TODO: 实现找后继
        Integer next = set.higherKey(x);
        return next==null?-1:next;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int q = scanner.nextInt();
        while (q-- > 0) {
            int op = scanner.nextInt();
            switch (op) {
                case 1:
                    insertValue(scanner.nextInt());
                    break;
                case 2:
                    eraseValue(scanner.nextInt());
                    break;
                case 3:
                    System.out.println(xCount(scanner.nextInt()));
                    break;
                case 4:
                    System.out.println(sizeOfSet());
                    break;
                case 5:
                    System.out.println(getPre(scanner.nextInt()));
                    break;
                case 6:
                    System.out.println(getBack(scanner.nextInt()));
                    break;
            }
        }
        scanner.close();
    }
}