求二叉樹最小結點

 struct BTNode
{
  int data;
  struct BTNode *lchild;
  struct BTNode *rchild;
}
BTNode * MinNode(BTNode *b){
    if (b != NULL){
        BTNode *min1, *min2, *min;
        if (b->lchild == NULL && b->rchild == NULL)
            return b;
        else if (b->lchild == NULL && b->rchild != NULL)    //右單支
            return MinNode(b->rchild);
        else if (b->lchild != NULL && b->rchild == NULL)    //左單支
            return MinNode(b->lchild);
        min1 = MinNode(b->lchild);
        min2 = MinNode(b->rchild);
        min = (min1->data) < (min2->data) ? min1 : min2;
        min = (min->data) < (b->data) ? min : b;
        return min;
    }
}