#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
using namespace std;
int key[10000],flag=0,root=-1;
int l[10000],r[10000];
void insert(int in,int x){
if(x<=key[in]){
if(l[in]==-1)l[in]=flag;
else insert(l[in],x);
}
else{
if(r[in]==-1)r[in]=flag;
else insert(r[in],x);
}
}
void order(int out){
if(l[out]!=-1)order(l[out]);
printf("the key is:%d ",out);
printf("%d\n",key[out]);
if(r[out]!=-1)order(r[out]);
}
int main(){
int i,j,k,m,n;
scanf("%d",&n);
int x;
flag=0,root=-1;
memset(l,-1,sizeof(l));
memset(r,-1,sizeof(r));
while(n--){
scanf("%d",&x);
if(root==-1)key[++root]=x;
else{
key[++flag]=x;
insert(root,x);
}
}
order(root);
return 0;
}
排序二叉树的原理其实十分简单,就是比根节点小的都放在左边,比根节点大的都放在右边,然后递归实现