臭代码如下，因为想练习一下class类，所以写成了这个亚子

#include<cstdio>

const int INF=2147483647;

int n;

class BSTnode {

private:

    int val,sum,size;

    BSTnode *lc,*rc,*parent;

    friend class BSTree;

public:

    BSTnode(int siz=0,int s=0,int k=0,BSTnode *ls=NULL,BSTnode *rs=NULL,BSTnode *par=NULL):

        size(siz),sum(s),val(k),lc(ls),rc(rs),parent(par) {};

};

class BSTree {

private://内部接口

    BSTnode *rt;

    BSTnode* Max(BSTnode *x) {

        while(x->rc!=NULL)x=x->rc;

        return x;

    }

    BSTnode* Min(BSTnode *x) {

        while(x->lc!=NULL)x=x->lc;

        return x;

    }

    BSTnode* Search(BSTnode *x,int key) {

        while(x!=NULL&&x->val!=key) {

            if(x->val>key)x=x->lc;

            else x=x->rc;

        }

        return x;

    }

    void Insert(BSTnode *&root,BSTnode *k) {

        BSTnode *x=root;

        BSTnode *y=NULL;

        while(x!=NULL) {

            x->size++;

            y=x;

            if(x->val<k->val) {

                x=x->rc;

            }

            else if(x->val==k->val) {

                x->sum++;

                return;

            }

            else {

                x=x->lc;

            }

        }

        k->parent=y;

        if(y==NULL) {

            root=k;

        } else if(y->val<k->val) {

            y->rc=k;

        } else y->lc=k;

    }

    int Find1(BSTnode *x,int key) {

        if(x==NULL)return 0;

        if(x->val==key)return (x->lc->size)+1;

        else if(x->val>key)return Find1(x->lc,key);

        else return Find1(x->rc,key)+(x->lc->size)+(x->sum);

    }

    int Find2(BSTnode *x,int key) {

        if(x->sum+x->lc->size>=key)return x->val;

        else if(x->val>key)return Find2(x->lc,key);

        else return Find2(x->rc,key-(x->sum)-(x->lc->size));

    }

    BSTnode* Pre(BSTnode *x) {

        BSTnode *y=NULL;

        if(x->lc!=NULL)return max(x->lc);

        y=x->parent;

        while(y!=NULL&&x==y->lc) {

            x=y;

            y=y->parent;

        }

        return y;

    }

    BSTnode* Next(BSTnode *x) {

        BSTnode *y=NULL;

        if(x->rc!=NULL)return min(x->rc);

        y=x->parent;

        while(y!=NULL&&x==y->rc) {

            x=y;

            y=y->parent;

        }

        return y;

    }

   /* void InOrder(BSTnode *x){

        if(x==NULL)return;

        InOrder(x->lc);

        printf("%d ",x->val);

        InOrder(x->rc);

    }*/

public://外部接口

    BSTree():rt(NULL) {};

    int find1(int key) {

        return Find1(rt,key);

    }

    int find2(int key) {

        return Find2(rt,key);

    }

    int pre(BSTnode *key) {

        BSTnode* tmp=Pre(key);

        if(tmp!=NULL)return tmp->val;

        return -INF;

    }

    int next(BSTnode *key) {

        BSTnode* tmp=Next(key);

        if(tmp!=NULL)return tmp->val;

        return INF;

    }

    BSTnode* search(int key) {

        return Search(rt,key);

    }

    BSTnode* max(BSTnode *x) {

        return Max(x);

    }

    BSTnode* min(BSTnode *x) {

        return Min(x);

    }

    void insert(int key) {

        BSTnode* tmp=new BSTnode(0,0,key,NULL,NULL,NULL);

        Insert(rt,tmp);

    }

   /* void inOrder(){

        InOrder(rt);

        printf("\n");

    }*/

};

int main() {

    scanf("%d",&n);

    BSTree *tree=new BSTree();

    int opt,k;

    for(int i=0;i<n;i++) {

        scanf("%d%d",&opt,&k);

        if(opt==1) {

            printf("%d\n",tree->find1(k));

        }

        else if(opt==2) {

            printf("%d\n",tree->find2(k));

        }

        else if(opt==3) {

            printf("%d\n",tree->pre(tree->search(k)));

        }

        else if(opt==4) {

            printf("%d\n",tree->next(tree->search(k)));

        }

        else if(opt==5) {

            tree->insert(k);

        }

        //tree->inOrder();

    }

    return 0;

}