指针是个好东西

不过就是得判空

还有别忘传引用（其实应该都传引用）

#include
    
     #include
     
      #include
      
       using namespace std;int inf=0x7fffffff;struct node* nil;struct node{    int num;    int val;    int size;    node* ch[2];    node (int v) :val(v)    {        size=1;        num=1;        ch[0]=ch[1]=nil;    }    void sum()    {        size=num;        if(ch[0]!=nil)            size+=ch[0]->size;        if(ch[1]!=nil)            size+=ch[1]->size;        return ;    }    int cmp(int v)    {        if(val==v)            return -1;        return (val>v ? 0 : 1);    }    int cmpkth(int k)    {        int s=( ch[0]==nil ? 0 : ch[0]->size );        if(k>s&&k<=s+num)            return -1;        if(k<=s)            return 0;        else            return 1;    }};node* root;void visit(node* x){    if(x==nil)        return ;    visit(x->ch[0]);    printf("%d ",x->val);    visit(x->ch[1]);    return ;}void rotato(node* &x,int base){    node* k=x->ch[base^1];    x->ch[base^1]=k->ch[base];    k->ch[base]=x;    x->sum();    k->sum();    x=k;}void splay(node* &x,int v){    int d=x->cmp(v);    if(d!=-1&&x->ch[d]!=nil)    {        int d2=x->ch[d]->cmp(v);        if(d2!=-1&&x->ch[d]->ch[d2]!=nil)        {            splay(x->ch[d]->ch[d2],v);            if(d==d2)                rotato(x,d2^1),rotato(x,d^1);            else                rotato(x->ch[d],d2^1),rotato(x,d^1);        }        else            rotato(x,d^1);    }}void splaykth(node* &x,int k){    int d=x->cmpkth(k);    if(d!=-1)    {        if(d==1)            k=k-x->ch[0]->size-x->num;        int d2=x->ch[d]->cmpkth(k);        if(d2!=-1)        {            int k2=(d2==1 ? k-x->ch[d]->ch[0]->size-x->ch[d]->num : k);            splaykth(x->ch[d]->ch[d2],k2);            if(d==d2)                rotato(x,d2^1),rotato(x,d^1);            else                rotato(x->ch[d],d2^1),rotato(x,d^1);        }        else            rotato(x,d^1);    }    return ;}void pre(node* x,int val,int &ans){    if(x==nil)        return ;    if(x->val
       
        val>ans)            ans=x->val;        if(x->ch[1]!=nil)            pre(x->ch[1],val,ans);    }    else        if(x->val>=val&&x->ch[0]!=nil)            pre(x->ch[0],val,ans);}void nxt(node* x,int val,int &ans){    if(x==nil)        return ;    if(x->val>val)    {        if(x->val
        
         val;        if(x->ch[0]!=nil)            nxt(x->ch[0],val,ans);    }    else        if(x->val<=val&&x->ch[1]!=nil)            nxt(x->ch[1],val,ans);}int find(node* &x,int val){    splay(x,val);    return x->ch[0]->size+1;}int kth(node* &x,int k){    splaykth(x,k);    return x->val;}node *spilt(node* &x,int val){    if(x==nil)        return nil;    splay(x,val);    node* t1;    node* t2;    if(x->val<=val)        t1=x,t2=x->ch[1],t1->ch[1]=nil;    else        t2=x,t1=x->ch[0],t2->ch[0]=nil;    x->sum();    x=t1;    return t2;}void merge(node* &t1,node* &t2){    if(t1==nil)        swap(t1,t2);    splay(t1,inf);    t1->ch[1]=t2;    t2=nil;    t1->sum();}void insert(node* &x,int val){    //visit(x);printf("\n");    node* t2=spilt(x,val);    //visit(x);printf("\n");    if(x!=nil&&x->val==val)    {        x->num+=1;        x->sum();    }    else    {        node* nw=new node(val);        merge(x,nw);    }    merge(x,t2);    //visit(root);printf("\n");}void erase(node* &x,int val){    node* t2=spilt(x,val);    x->num-=1;    if(x->num==0)    {        node* t3=x;        x=x->ch[0];        delete t3;    }    merge(x,t2);}int read(){    int s=0,f=1;    char in=getchar();    while(in<'0'||in>'9')    {        if(in=='-')            f=-1;        in=getchar();    }    while(in>='0'&&in<='9')    {        s=(s<<1)+(s<<3)+in-'0';        in=getchar();    }    return s*f;}int main(){    int n=read();    int a,b;    int ans;    nil=new node(0);    root=nil->ch[0]=nil->ch[1]=nil;    nil->size=nil->num=0;    for(int i=1;i<=n;i++)    {        a=read();        b=read();        switch(a)        {            case 1: insert(root,b);break;            case 2: erase(root,b);break;            case 3: printf("%d\n",find(root,b));break;            case 4: printf("%d\n",kth(root,b));break;            case 5: insert(root,b);ans=-0x7fffffff;pre(root,b,ans);printf("%d\n",ans);erase(root,b);break;            case 6: insert(root,b);ans=0x7fffffff;nxt(root,b,ans);printf("%d\n",ans);erase(root,b);break;            default: break;        }    }    return 0;}