求助，rt，上代码：

import java.util.Scanner;
import java.util.ArrayList;

public class Main {
    static Scanner sc=new Scanner(System.in);
    static int bound=0;
    static class tree{
        int root;
        int size;
        int rep;
        tree father;
        tree Lchild;
        tree Rchild;
        public tree(){
            this.root=0;
            this.rep=1;
            this.size=0;
            this.father=null;
            this.Lchild=null;
            this.Rchild=null;
        }
        public void append(int val){
            if(val==this.root){
                this.rep++;
                this.size++;
                return;
            }
            if(this.isEmpty()){
                this.root=val;
            }
            else{
                if(val>this.root){
                    if(this.Rchild==null){
                        this.Rchild=new tree();
                        Rchild.father=this;
                    }
                    Rchild.append(val);
                }
                else{
                    if(this.Lchild==null){
                        this.Lchild=new tree();
                        Lchild.father=this;
                    }
                    Lchild.append(val);
                }
            }
            this.size++;
        }
        public boolean isFull(){
            return(this.Lchild!=null && this.Rchild!=null);
        }
        public boolean isEmpty(){
            int m=this.size;
            return(m==0);
        }
        public boolean isLeaf(){
            return(this.Lchild==null && this.Rchild==null);
        }
        public int getLChildSize(){
            if(this.Lchild==null){
                return(0);
            }
            else{
                return(this.Lchild.size);
            }
        }
        public int getRChildSize(){
            if(this.Rchild==null){
                return(0);
            }
            else{
                return(this.Rchild.size);
            }
        }
        public int getNum(int pos){
            if(pos>this.getLChildSize() && pos<=this.getLChildSize()+this.rep){
                return(this.root);
            }
            else if(pos<=this.getLChildSize()){
                return(Lchild.getNum(pos));
            }
            else{
                pos-=this.rep;
                pos-=this.getLChildSize();
                return(Rchild.getNum(pos));
            }
        }
        public int getPos(int num){
            if(num==this.root){
                if(this.Lchild==null){
                    return(1);
                }
                return(this.Lchild.size+1);
            }
            else if(num<this.root){
                return(this.Lchild.getPos(num));
            }
            else{
                if(this.Lchild==null){
                    return(this.rep+this.Rchild.getPos(num));
                }
                return(this.Lchild.size+this.rep+this.Rchild.getPos(num));
            }
        }
        public int getPrev(){
            if(this.Lchild==null){
                if(this.father.root<this.root){
                    return(this.father.root);
                }
                else{
                    return(-2147483647);
                }
            }
            else{
                return(this.Lchild.getNum(this.Lchild.size));
            }
        }
        public int getPrev(int num){
            if(num==this.root){
                return(this.getPrev());
            }
            else if(num<this.root){
                try{
                    return(this.Lchild.getPrev(num));
                }
                catch(NullPointerException ex){
                    return(-2147483647);
                }
            }
            else{
                try{
                    return(this.Rchild.getPrev(num));
                }
                catch(NullPointerException ex){
                    return(-2147483647);
                }
            }
        }
        public int getNext(){
            if(this.Rchild==null){
                if(this.father.root>this.root){
                    return(this.father.root);
                }
                else{
                    return(-2147483647);
                }
            }
            else{
                return(this.Rchild.getNum(1));
            }
        }
        public int getNext(int num){
            if(num==this.root){
                return(this.getNext());
            }
            else if(num<this.root){
                try{
                    return(this.Lchild.getNext(num));
                }
                catch(NullPointerException ex){
                    return(-2147483647);
                }
            }
            else{
                try{
                    return(this.Rchild.getNext(num));
                }
                catch(NullPointerException ex){
                    return(-2147483647);
                }
            }
        }
    }
    public static void main(String[] args){
        tree home=new tree();
        int count=sc.nextInt();
        int[] comm=new int[count];
        int[] param=new int[count];
        for(int i=0;i<count;i++){
            comm[i]=sc.nextInt();
            param[i]=sc.nextInt();
        }
        for(int i=0;i<count;i++){
            inner:switch(comm[i]){
                case(1):{
                    System.out.println(home.getPos(param[i]));
                    break inner;
                }
                case(2):{
                    System.out.println(home.getNum(param[i]));
                    break inner;
                }
                case(3):{
                    System.out.println(home.getPrev(param[i]));
                    break inner;
                }
                case(4):{
                    System.out.println(home.getNext(param[i]));
                    break inner;
                }
                case(5):{
                    home.append(param[i]);
                    break inner;
                }
                
            }
        }
    }
}