程序代码：

#define EL 10
#define TEL 2*EL+1
#define LEN sizeof(struct node)
#include<stdio.h>
#include<stdlib.h>
char pre[TEL]="abdhiecfg";
char pin[TEL]="hdibeafcg";
typedef struct node{
    char data;
    struct node * lch,*rch;
}BTNode,*BTree;
BTNode root;
BTree rt=&root;
int pos(char c,char s[],int st){
    char *p;
    p=s+st;
    while(*p!=c && *p!='\0') 
        p++;
    return p-s;
}
void create(BTree *t,int i1,int i2,int len){
    int r,llen,rlen;
    if(len<=0) 
        *t=NULL;
    else{
        *t=(BTree)malloc(LEN);
        (*t)->data=pre[i1];
        r=pos(pre[i1],pin,i2);
        llen=r-i2;
        rlen=len-(llen+1);
        create(&(*t)->lch,i1+1,i2,llen);
        create(&(*t)->rch,i1+llen+1,r+1,rlen);
    }
}

void travel(BTree t){
    if(t){
        travel(t->lch);
        travel(t->rch);
        putchar(t->data);
    }
}

void main(){
    create(&rt,0,0,EL);
    if(rt) 
        travel(rt);
    printf("\n");
}