只有60分

代码：

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int inf=1e9+7;
int n,r=0,num[1000005],siz[10000005],son[10000005][2],rd[10000005],val[10000005],tot;
void pushup(int x){
	siz[x]=siz[son[x][0]]+siz[son[x][1]]+num[x];
}
void rotate(int &p,int d){
	int k=son[p][d^1];
	son[p][d^1]=son[k][d];
	son[k][d]=p;
	pushup(p);
	pushup(k);
	p=k;
}
void insert(int &p,int x){
	if(!p){
		p=++tot;
		siz[p]=num[p]=1;
		val[p]=x;
		rd[p]=rand();
		return;
	}
	else if(val[p]==x){
		num[x]++;
		siz[x]++;
		return;
	}
	else{
		int d=(x>val[p]);
		insert(son[p][d],x);
		if(rd[p]<rd[son[p][d]]) rotate(p,d^1);
	}
	pushup(p);
}
void del(int &p,int x){
	if(!p) return;
	if(x>val[p]) del(son[p][1],x);
	else if(x<val[p]) del(son[p][0],x);
	else{
		if(!son[p][0]&&!son[p][1]){
			num[p]--,siz[p]--;
			if(!num[p]) p=0;
		}
		else if(son[p][0]&&!son[p][1]){
			rotate(p,1);
			del(son[p][1],x);
		}
		else if(!son[p][0]&&son[p][1]){
			rotate(p,0);
			del(son[p][0],x);
		}
		else{
			int d=(rd[son[p][0]]>rd[son[p][1]]);
			rotate(p,d);
			del(son[p][d],x);
		}
	}
	pushup(p);
}
int rnk(int p,int x){
	if(!p) return 0;
	if(val[p]==x) return siz[son[p][0]]+1;
	else if(val[p]>x) return rnk(son[p][0],x);
	else return rnk(son[p][1],x)+siz[son[p][0]]+num[p];
}
int kth(int p,int x){
	if(!p) return 0;
	if(x<=siz[son[p][0]]) return kth(son[p][0],x);
	else if(x>siz[son[p][0]]+num[p]) return kth(son[p][1],x-siz[son[p][0]]-num[p]);
	else return val[p];
}
int pre(int p,int x){
	if(!p) return -inf;
	if(x<=val[p]) return pre(son[p][0],x);
	else return max(val[p],pre(son[p][1],x));
}
int lst(int p,int x){
	if(!p) return inf;
	if(x>=val[p]) return lst(son[p][1],x);
	else return min(val[p],lst(son[p][0],x));
}
signed main(){
	//freopen("a.txt","r",stdin);
	//freopen("b.txt","w",stdout);
	cin>>n;
	for(int i=1;i<=n;i++){
		int opt;
		cin>>opt;
		if(opt==1){
			int x;
			cin>>x;
			insert(r,x);
		}
		else if(opt==2){
			int x;
			cin>>x;
			del(r,x);
		}
		else if(opt==3){
			int x;
			cin>>x;
			cout<<rnk(r,x)<<endl;
		}
		else if(opt==4){
			int x;
			cin>>x;
			cout<<kth(r,x)<<endl;
		}
		else if(opt==5){
			int x;
			cin>>x;
			cout<<pre(r,x)<<endl;
		}
		else{
			int x;
			cin>>x;
			cout<<lst(r,x)<<endl;
		}
	}
	return 0;
}