前序ABFGCHDEIJLK求二叉树

#define EL 12
#define TEL 2*EL+1
#define LEN sizeof(struct node)
#include<stdio.h>

char pre[TEL]="ABFGCHDEIJLK";
char pin[TEL]="FGBHCDILJKEA";

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);
}