非旋Treap——fhq treap

https://www.luogu.org/problemnew/show/P3369

知识点：1.拆分split,合并merge

　　　　2.split,merge要点：通过传址调用来简便代码

　　　　3.记得root = merge(xxxxx,xxxxx);

2 wrong in code

#include <bits/stdc++.h>
#define M 200002
using namespace std;
int tot = 0;
int val[M],rd[M];
int ch[M][2];
int root = 0;
int m;
int siz[M];
int newnode(int x)
{
    siz[++tot] = 1;
    val[tot] = x;
    rd[tot] = rand();
    return tot;
}
void updata(int x)
{
    siz[x] = siz[ch[x][0]] + siz[ch[x][1]] + 1;
}
void split(int now,int k,int &x,int &y)
{
    if(!now)
    {
        x = y = 0;
        return;
    }
    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]);
        }
        updata(now);
    }
}
int merge(int A,int B)
{
    if(!A || !B) return  A + B;
    if(rd[A] < rd[B]){ch[A][1] = merge(ch[A][1],B); updata(A); return A;}
    else {ch[B][0] = merge(A,ch[B][0]); updata(B); return B;} 
}
void insert(int t)
{
    int x,y;
    split(root,t,x,y);
    root = merge(merge(x,newnode(t)),y);
}
void del(int t)
{
    int x,y,z;
    split(root,t,x,z);
    split(x,t - 1,x,y);//wrong 1:是 split(x,t - 1,x,y)而不是 split(root,t - 1,x,y)
    y = merge(ch[y][0],ch[y][1]);//wrong 2: 记得y =  
    root = merge(merge(x,y),z);
}
int findrk(int t)
{
    int x,y;
    split(root,t - 1,x,y);
    int ans = siz[x] + 1;
    root = merge(x,y);
    return ans;
}
int kth(int now,int k)
{
    while(now)
    {
        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];
    }
    return now;
}
int front(int k)
{
    int x,y;
    split(root,k - 1,x,y);
    int ans = val[kth(x,siz[x])];
    root = merge(x,y);
    return ans; 
}
int back(int k)
{
    int x,y;
    split(root,k,x,y);
    int ans = val[kth(y,1)];
    root = merge(x,y);
    return ans;
}
int main()
{
    srand(1);
    scanf("%d",&m);
    int x,y;
    while(m--)
    {
        scanf("%d%d",&x,&y);
        if(x == 1)
        {
            insert(y);
        }
        if(x == 2)
        {
            del(y);
        }
        if(x == 3)
        {
            printf("%d
",findrk(y));
        }
        if(x == 4)
        {
            printf("%d
",val[kth(root,y)]);
        }
        if(x == 5)
        {
            printf("%d
",front(y));
        }
        if(x == 6)
        {
            printf("%d
",back(y));
        }
    }
    return 0;
}