求出给定二叉排序树的最小值和最大值

KeyType MinKey)(BSTNode *bt){
    while(bt->lchild!=NULL){
        bt=bt->lchild;
    }
    return bt->data;
}
KeyType MaxKey)(BSTNode *bt){
    while(bt->rchild!=NULL){
        bt=bt->rchild;
    }
    return bt->data;
}