普通平衡树 Treap

Code：

#include<cstdio>
#include<cstdlib>
#include<algorithm>
using namespace std;
struct Node{
    Node *ch[2];
    int r,v,s,val;
    int cmp(int x) const{
        if(x==v)return -1;
        return x<v?0:1;
    }
    Node(int V){
        s=1,val=1;ch[0]=ch[1]=NULL;
        r=rand();v=V;
    }
    void maintain(){
        s=val;
        if(ch[0]!=NULL)s+=ch[0]->s;
        if(ch[1]!=NULL)s+=ch[1]->s;
    }
};
Node *head;
void rotate(Node* &o,int d){
    Node *k=o->ch[d^1];o->ch[d^1]=k->ch[d];k->ch[d]=o;
    o->maintain();k->maintain();o=k;
}
void insert(Node* &o,int x){
    if(o==NULL)o=new Node(x);
    else{
        int d=o->cmp(x);
        if(d==-1){
            ++(o->val);++(o->s);return;
        }
        insert(o->ch[d],x);
        o->maintain();
        if((o->ch[d]->r)>o->r)rotate(o,d^1);
    }
}
void erase(Node* &o,int x){
    int d=o->cmp(x);
    if(d==-1){
        if(o->ch[0]==NULL){
            (o->val)--;(o->s)--;
            if(o->val==0)o=o->ch[1];
        }
        else if(o->ch[1]==NULL){
            (o->val)--;(o->s)--;
            if(o->val==0)o=o->ch[0];
        }
        else{
            int d2=(o->ch[0]->r)>(o->ch[1]->r)?1:0;
            rotate(o,d2);
            erase(o->ch[d2],x);
            o->maintain();
        }
    }else {
        erase(o->ch[d],x);
        o->maintain();
    }
}
int rank1(Node *o,int x){                  //x的排名
    int d=o->cmp(x);
    int lsize=(o->ch[0]==NULL)?0:o->ch[0]->s;
    if(d==0)return rank1(o->ch[0],x);
    if(d==1)return lsize+o->val+rank1(o->ch[1],x);
    return lsize+1;
}
int kth(Node *o,int R){                    //第k大
    int lsize=(o->ch[0]==NULL)?0:o->ch[0]->s;
    if(R<=lsize)return kth(o->ch[0],R);
    if(lsize+o->val>=R)return o->v;
    return kth(o->ch[1],R-lsize-o->val);
}
int ans;
void find1(Node *o,int x){                //前驱
    if(o->v<x){ans=max(ans,o->v);if(o->ch[1]!=NULL)find1(o->ch[1],x);}
    else if(o->ch[0]!=NULL)find1(o->ch[0],x);
}
void find2(Node *o,int x){                //后继
    if(o->v>x){ans=min(ans,o->v);if(o->ch[0]!=NULL)find2(o->ch[0],x);}
    else if(o->ch[1]!=NULL)find2(o->ch[1],x);
}
int main()
{
    int n;
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
    {
        int opt,x;
        scanf("%d%d",&opt,&x);
        if(opt==1)insert(head,x);
        if(opt==2)erase(head,x);
        if(opt==3)printf("%d\n",rank1(head,x));
        if(opt==4)printf("%d\n",kth(head,x));
        if(opt==5){ans=-10000000;find1(head,x);printf("%d\n",ans);}
        if(opt==6){ans=10000000;find2(head,x);printf("%d\n",ans);}
    }
    return 0;
}