Tree *create()//前序递归创建二叉树
{
    Tree *head=new Tree;
    char c;
    cin>>c;
    if(c=='#')
        head=NULL;
    else
    {
        head->data=c;
        head->left=create();//创建左子树
        if(head->left==NULL)
            head->l=0;//左子树为空
        head->right=create();//创建右子树
        if(head->right==NULL)
            head->r=0;//右子树为空
    }
    return head;
}