题解 | 【模板】多重集合操作

import java.util.*;

public class Main {
    private static TreeMap<Integer,Integer> hashMap=new TreeMap<>();
    private static int total=0;//注意必须用，用来计算数量，如果自己调用方法计算，则会超时

    public static void insertValue(int x) {
        // TODO: 实现插入逻辑
        if(hashMap.containsKey(x)){
            hashMap.put(x,hashMap.get(x)+1);
            total++;
        }else{
            hashMap.put(x,1);
            total++;
        }
        
    }

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

        }

    }

    public static int xCount(int x) {
        // TODO: 求x在集合中的个数
        return hashMap.getOrDefault(x,0);
    }

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

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

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

    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();
    }
}