【模板】普通平衡树 Treap

#include<iostream> 
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<cstring>
using namespace std;
const int N=100010,inf=10000010;
int n;

struct node
{
    node* ch[2];
    int r,s,v;
    node(int v):v(v){s=1; r=rand(); ch[0]=ch[1]=NULL;}
    bool operator < (const node& rhs) const {return r < rhs.r;}
    int cmp(int x){if(x == v)return -1; return x < v ? 0 : 1 ;}
    void maintain(){s=1;
        if(ch[0] != NULL) s+=ch[0]->s; if(ch[1] != NULL) s+=ch[1]->s;
    }
};
node* rt=NULL;

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 ins(node* &o,int x){
    if(o == NULL){o=new node(x);return ;}
    int d=(x < o->v ? 0 : 1);ins(o->ch[d],x);
    if(o->ch[d] > o) rotate(o,d^1); o->maintain();
}
void del(node* &o,int x){
    if(o == NULL) return ;
    int d=o->cmp(x);
    if(d == -1){
        if(o->ch[0] != NULL && o->ch[1] != NULL){
            int d2=(o->ch[1]->r > o->ch[0]->r ? 0 : 1);
            rotate(o,d2);del(o->ch[d2],x);
        }
        else {if(o->ch[0] == NULL) o=o->ch[1];else o=o->ch[0];}
    }
    else del(o->ch[d],x); if(o != NULL) o->maintain();
}

int kth(node *o,int k){
    if(o == NULL || k > o->s || o <= 0) return 0;
    int s=(o->ch[0] == NULL ? 0 : o->ch[0]->s);
    if(k == s+1) return o->v;
    if(k <= s) return kth(o->ch[0], k);
    return kth(o->ch[1], k-s-1);
}
void rank(node *o,int x,int &ans,int k){
    if(o==NULL) return ;
    int ss=(o->ch[0] == NULL ? 0 : o->ch[0]->s);
    if(o->v < x) {rank(o->ch[1],x,ans,k+ss+1); return ;}
    if(o->v == x) ans=min(ans,k+ss+1);
    rank(o->ch[0],x,ans,k);
}
void pre(node* o,int x,int &ans){
    if(o == NULL) return ;
    if(o->v < x) {ans=max(o->v, ans); pre(o->ch[1],x,ans); return ;}
    pre(o->ch[0],x,ans); 
}
void post(node* o,int x,int &ans){
    if(o == NULL) return ;
    if(o->v > x) {ans=min(o->v, ans); post(o->ch[0], x, ans); return ;}
    post(o->ch[1], x, ans); 
}

void solve(){
    n=read();
    while(n--){
        int opt=read(),x=read();
        if(opt == 1) ins(rt, x);
        if(opt == 2) del(rt, x);
        if(opt == 4) printf("%d
",kth(rt, x));
        if(opt == 3) {int ans3=inf; rank(rt, x,ans3,0); printf("%d
",ans3);}
        if(opt == 5) {int ans5=-inf; pre(rt, x,ans5); printf("%d
",ans5);}
        if(opt == 6) {int ans6=inf; post(rt, x,ans6); printf("%d
",ans6);}
    }
}