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自测了RE样例没问题呀

#include<iostream>
#include<algorithm>
#include<cstdlib>
using namespace std;
struct Node{
	Node *zs[2];
	int size,val,repcnt,prio;
	Node(int val): val(val),repcnt(1),size(1){
		zs[0]=zs[1]=nullptr;
		prio=rand();
	}
	void upd_size(){
		size=repcnt;
		if(zs[0]!=nullptr)size+=zs[0]->size;
		if(zs[1]!=nullptr)size+=zs[1]->size;
	}
};

void rotate(Node *&cur,int dir){
	//以下注释以左旋为例 
	Node *tmp=cur->zs[dir]; //将tmp设为cur的右孩子 
	cur->zs[dir]=tmp->zs[!dir]; //cur与tmp断裂，连接到tmp的左孩子 
	tmp->zs[!dir]=cur; //tmp成为根
	tmp->upd_size();
	cur->upd_size();//更新大小 
	cur=tmp;
} 

void insert(Node *&cur,int val){
	if(cur==nullptr){   //新建 
		cur=new Node(val);
		return;
	}else if(val==cur->val){   //发现有重复的
		cur->repcnt++;
		cur->size++; 
	}else if(val<cur->val){   //插左边
		insert(cur->zs[0],val);
		if(cur->zs[0]->prio<cur->prio){
			//左边比根小，右旋
			rotate(cur,0); 
		} 
		cur->upd_size();
	}else if(val>cur->val){   //插右边
		insert(cur->zs[1],val);
		if(cur->zs[1]->prio<cur->prio) {
			rotate(cur,1);
		}
		cur->upd_size();
	}
} 

void erase(Node *&cur,int val){
	if(val<cur->val){
		erase(cur->zs[0],val);
		cur->upd_size();
	}else if(val>cur->val){
		erase(cur->zs[1],val);
		cur->upd_size();
	}else{
		if(cur->repcnt>1){  //如果不止一个，直接减 
			cur->repcnt--;
			cur->size--;
			return;
		}
		uint8_t st=0;
		st|=(cur->zs[0]!=nullptr);
		st|=((cur->zs[1]!=nullptr)<<1);
		//二进制，00都无，10有右无左，01有左无右，11都有 
		Node *tmp=cur;
		switch(st){
			case 0:
				delete cur;
				cur=nullptr;
				break;
			case 1:
				cur=tmp->zs[0];
				delete tmp;
				break;
			case 2:
				cur=tmp->zs[1];
				delete tmp;
				break;
			case 3:
				int dir;
				if(cur->zs[0]->prio>cur->zs[1]->prio){
					dir=1;
				}else{
					dir=0;
				}
				rotate(cur,dir);
				erase(cur->zs[!dir],val);
				cur->upd_size();
				break;
		}
	}
}

int frank(Node *&cur,int val){
	int lesize=cur->zs[0]==nullptr?0 : cur->zs[0]->size;
	//子树中比val小的结点的数量
	if(val==cur->val){
		return lesize+1;
	}else if(val<cur->val){
		return frank(cur->zs[0],val);
	}else{
		return lesize+cur->repcnt+frank(cur->zs[1],val);
	}
} 

int getv(Node *&cur,int rank){
	int lesize=cur->zs[0]==nullptr?0 : cur->zs[0]->size;
	if(rank<=lesize){
		return getv(cur->zs[0],rank);
	}else if(rank<=cur->repcnt+lesize){
		return cur->val;
	}else{
		return getv(cur->zs[1],rank-lesize-cur->repcnt);
	}
}
int pre_ans,nex_ans;
int pre(Node *&cur,int val){
	if(val<=cur->val){
		if(cur->zs[0]!=nullptr)return pre(cur->zs[0],val);
	}else{
		pre_ans=cur->val;
		if(cur->zs[1]!=nullptr)pre(cur->zs[1],val);
		return pre_ans;
	}
}

int next(Node *&cur,int val){
	if(val>=cur->val){
		if(cur->zs[1]!=nullptr)return next(cur->zs[1],val);
	}else{
		nex_ans=cur->val;
		if(cur->zs[0]!=nullptr)next(cur->zs[0],val);
		return nex_ans;
	}
}

int main(){
	int n;
	cin >> n;
	Node *root=nullptr;
	for(int i=1;i<=n;i++){
		int opt,x;
		cin >> opt >> x;
		switch(opt){
			case 1:insert(root,x);break;
			case 2:erase(root,x);break;
			case 3:cout << frank(root,x) <<"\n";break;
			case 4:cout << getv(root,x) <<"\n";break;
			case 5:cout << pre(root,x) <<"\n";break;
			case 6:cout << next(root,x) <<"\n";break;
		}
	}
	return 0;
}