注意要插入的值，如果等于当前节点，就把它变成当前节点的右儿子

此代码是中南大学暑训入门 B题的AC代码

#include
     
      #define ll long longusing namespace std;struct node{    ll data;    node * lson;    node * rson;}*head;int t;void build(ll x,node *p){    if(p==NULL){        node * pp;        pp=new node ;        pp->data=x;        pp->lson=NULL;        pp->rson=NULL;        head=pp;        return;    }    if(p->data<=x&&p->rson){build(x,p->rson);}    else if(p->data>x&&p->lson){build(x,p->lson);}    else if(p->data<=x&&!p->rson){        node * pp;        pp=new node ;        pp->data=x;        pp->lson=NULL;        pp->rson=NULL;        p->rson=pp;    }    else if(p->data>x&&!p->lson){        node * pp;        pp=new node ;        pp->data=x;        pp->lson=NULL;        pp->rson=NULL;        p->lson=pp;    }}void preview(node *p){    if(p==NULL){return;}    if(t){cout<<" ";}    cout<
      
       data;t++;    preview(p->lson);    preview(p->rson);}void midview(node *p){    if(p==NULL){return;}    midview(p->lson);    if(t)cout<<" ";    cout<
       
        data;t++;    midview(p->rson);}void posview(node *p){    if(p==NULL){return;}    posview(p->lson);    posview(p->rson);    if(t){cout<<" ";}    cout<
        
         data;t++;}void delet(node *p){    if(p==NULL){return;}    delet(p->lson);    delet(p->rson);    delete p;}int main(){    int T;    while(cin>>T)    while(T--){        int n;        ll x;        cin>>n;        head=NULL;        for(int i=0;i
         
          >x;            build(x,head);        }        t=0;        preview(head);        cout<