fhq treap

https://www.cnblogs.com/zwfymqz/p/7151959.html
https://www.luogu.com.cn/problem/solution/P3369?page=2

#include 
using namespace std;
const int maxn = 5e5+100;
int ch[maxn][2],pri[maxn],siz[maxn],sz,val[maxn];
int root = 0,x,y,z;
int inline read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
inline void update(int x){
    siz[x] = 1+siz[ch[x][0]] +siz[ch[x][1]];
}
inline int new_node(int v){
    siz[++sz] = 1;
    val[sz] = v;
    pri[sz] = rand();
    return sz;
}
void split(int now,int k,int &x,int &y){
    if(!now) x = y = 0;
    else{
        if (val[now]<=k){
            x = now;
            split(ch[now][1],k,ch[now][1],y);
        }
        else{
            y = now;
            split(ch[now][0],k,x,ch[now][0]);
        }
        update(now);
    }
}
int merge(int x,int y){
    if (!x || !y) return x+y;
    if (pri[x]<pri[y]){
        ch[x][1] =merge(ch[x][1],y);
        update(x);
        return x;
    }
    else{
        ch[y][0] = merge(x,ch[y][0]);
        update(y);
        return y;
    }
}
int kth(int now,int k){
    while (1){
        if (k<=siz[ch[now][0]]) now = ch[now][0];
        else if (k == siz[ch[now][0]]+1) return now;
        else k-=siz[ch[now][0]]+1,now = ch[now][1];
    }
}
int main(){
    srand((unsigned)time(NULL));
    int t;
    t = read();
    while (t--){
        int opt,a;
        opt = read();
        a = read();
        if (opt == 1){
            split(root,a,x,y);
            root = merge(merge(x,new_node(a)),y);
        } else
        if (opt == 2){
            split(root,a,x,z);
            split(x,a-1,x,y);
            y =  merge(ch[y][0],ch[y][1]);
            root = merge(merge(x,y),z);
        } else
        if (opt == 3){
            split(root,a-1,x,y);
            printf("%d\n",siz[x]+1);
            root = merge(x,y);
        } else
        if (opt==4){
            printf("%d\n",val[kth(root,a)]);
        }else
        if (opt == 5){
            split(root,a-1,x,y);
            printf("%d\n",val[kth(x,siz[x])]);
            root = merge(x,y);
        }
        else{
            split(root,a,x,y);
            printf("%d\n",val[kth(y,1)]);
            root = merge(x,y);
        }
    }
}