題面在這裡

平衡樹裸題……
寫了Treap/非旋轉Treap兩個版本。

【普通Treap】

#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=100005,INF=0x3f3f3f3f;
int q;
struct node{
    node* s[2];
    int k,f,size,cnt;
    void maintain() {size=s[0]->size+s[1]->size+cnt;}
};
typedef node* P_node;
struct
 
 treap{
    node tree[maxn],nil;
    P_node null,len,root;
    treap(){
        root=null=&nil;
        null->s[0]=null->s[1]=null;
        null->size=null->cnt=0;
        len=tree;
    }
    P_node newnode(int key){
        len->k=key;len->f=rand();
        len->s[0]=len->s[1
 
]=null;
        len->size=len->cnt=1;
        return len++;
    }
    void rot(P_node &x,int d){
        P_node k=x->s[d^1];x->s[d^1]=k->s[d];k->s[d]=x;
        x->maintain();k->maintain();x=k;
    }
    void insert(P_node &x,int key){
        if (x==null) x=newnode(key);else
 

        if (x->k==key) x->cnt++;else{
            int d=key>x->k;
            insert(x->s[d],key);if (x->s[d]->f > x->f) rot(x,d^1);
        }
        x->maintain();
    }
    void erase(P_node &x,int key){
        if (x->k==key){
            if (x->cnt>1) x->cnt--;else
             if (x->s[0]==null) x=x->s[1];else
             if (x->s[1]==null) x=x->s[0];else{
                int d=x->s[0]->f < x->s[1]->f;
                rot(x,d^1);erase(x->s[d^1],key);
             }
        }else erase(x->s[key>x->k],key);
        x->maintain();
    }
    int kth(P_node &x,int k){
        if (x==null||k<1||k>x->size) return 0;
        if (k<=x->s[0]->size) return kth(x->s[0],k);else
        if (k>x->s[0]->size+x->cnt) return kth(x->s[1],k-x->s[0]->size-x->cnt);
        return x->k;
    }
    int rank(P_node &x,int key){
        if (x->k==key) return x->s[0]->size+1;
        if (key<x->k) return rank(x->s[0],key);
        return rank(x->s[1],key)+x->s[0]->size+x->cnt;
    }
    int pred(P_node &x,int key){
        if (x==null) return -INF;
        if (key<=x->k) return pred(x->s[0],key);
        return max(x->k,pred(x->s[1],key));
    }
    int succ(P_node &x,int key){
        if (x==null) return INF;
        if (key>=x->k) return succ(x->s[1],key);
        return min(x->k,succ(x->s[0],key));
    }
    void print(P_node &x){
        if (x==null) return;
        print(x->s[0]);
        for (int i=1;i<=x->cnt;i++) printf("%d ",x->k);
        print(x->s[1]);
    }
    void Insert(int x) {insert(root,x);}
    void Erase(int x) {erase(root,x);}
    int Rank(int x) {return rank(root,x);}
    int Kth(int x) {return kth(root,x);}
    int Pred(int x) {return pred(root,x);}
    int Succ(int x) {return succ(root,x);}
    void Print() {print(root);printf("**\n");}
}T;
inline int red(){
    int tot=0,f=1;char ch=getchar();
    while (ch<'0'||'9'<ch) {if (ch=='-') f=-f;ch=getchar();}
    while ('0'<=ch&&ch<='9') tot=tot*10+ch-48,ch=getchar();
    return tot*f;
}
int main(){
    q=red();
    while (q--){
        int c=red(),x=red();
        if (c==1) T.Insert(x);else
        if (c==2) T.Erase(x);else
        if (c==3) printf("%d\n",T.Rank(x));else
        if (c==4) printf("%d\n",T.Kth(x));else
        if (c==5) printf("%d\n",T.Pred(x));else
        if (c==6) printf("%d\n",T.Succ(x));
    }
    return 0;
}

【非旋轉Treap】

#include<cstdio>
#include<cstdlib>
const int maxn=100005;
struct node{
    node *s[2];
    int k,f,siz;
    node () {}
    node (int w,node *son) {s[0]=s[1]=son;k=w;f=rand();siz=1;}
    void pushup() {siz=s[0]->siz+s[1]->siz+1;}
}nil,base[maxn];
typedef node* P_node;
P_node null,len,Root;
void treap_init(){
    nil=node(0,NULL);null=&nil;
    null->s[0]=null->s[1]=null;
    null->siz=0; len=base; Root=null;
}
P_node newnode(int x){
    *len=node(x,null);
    return len++;
}
P_node merge(P_node a,P_node b){
    if (a==null) return b;
    if (b==null) return a;
    if (a->f > b->f) {a->s[1]=merge(a->s[1],b); a->pushup(); return a;}
    b->s[0]=merge(a,b->s[0]); b->pushup(); return b;
}
void split(P_node x,int k,P_node &l,P_node &r){
    if (x==null) {l=r=null;return;}
    if (x->k <= k) {l=x;split(l->s[1],k,l->s[1],r);}else
     {r=x;split(r->s[0],k,l,r->s[0]);}
    x->pushup();
}
void Insert(int k){
    P_node l,r;
    split(Root,k,l,r);
    Root=merge(merge(l,newnode(k)),r);
}
void Erase(int k){
    P_node l,mid,r;
    split(Root,k-1,l,r);split(r,k,mid,r);
    Root=merge(l,merge(merge(mid->s[0],mid->s[1]),r));
}
int Kth(P_node x,int k){
    if (k <= x->s[0]->siz) return Kth(x->s[0],k);else
    if (k > x->s[0]->siz+1) return Kth(x->s[1],k - x->s[0]->siz -1);
    return x->k;
}
int get_edge(P_node x,int d){
    while (x->s[d]!=null) x=x->s[d];
    return x->k;
}
int q;
inline int red(){
    int tot=0,f=1;char ch=getchar();
    while (ch<'0'||'9'<ch) {if (ch=='-') f=-f;ch=getchar();}
    while ('0'<=ch&&ch<='9') tot=tot*10+ch-48,ch=getchar();
    return tot*f;
}
int main(){
    treap_init();
    q=red();
    while (q--){
        int c=red();
        if (c==1) Insert(red());else
        if (c==2) Erase(red());else
        if (c==3){
            int k=red();P_node l,r;
            split(Root,k-1,l,r); printf("%d\n",l->siz+1); Root=merge(l,r);
        }else
        if (c==4) printf("%d\n",Kth(Root,red()));else
        if (c==5){
            int k=red();P_node l,r;
            split(Root,k-1,l,r); printf("%d\n",get_edge(l,1)); Root=merge(l,r);
        }else{
            int k=red();P_node l,r;
            split(Root,k,l,r); printf("%d\n",get_edge(r,0)); Root=merge(l,r);
        }
    }
    return 0;
}