AVL树（高度平衡的二叉搜索树）平衡因子的调节和旋转_avl可以不调整最小因子吗

template <typename K,typename V>
struct AVLTreeNode
{
	K _key;
	V _value;
	int _bf; //平衡因子,只能取值为-1,1,0
	AVLTreeNode<K, V>* _left;
	AVLTreeNode<K, V>* _right;
	AVLTreeNode<K, V>* _parent;
	AVLTreeNode(const K& key, const V& value)
		:_key(key)
		, _value(value)
		, _bf(0)
		, _left(NULL)
		, _right(NULL)
		, _parent(NULL)
	{}
};

void _RotateL(Node* &parent)
	{
		//1.将要修改的结点标记起来
		Node* SubR = parent->_right;
		Node* SubRL = SubR->_left;
		Node* pparent = parent->_parent;
		//2.重新链上SubR结点
		SubR->_left = parent;
		SubR->_parent = pparent;
		SubR->_bf = 0;
		//4.重新链上parent结点
		parent->_right = SubRL;
		parent->_parent = SubR;
		parent->_bf = 0;
		//5.改变pparent的指向结点
		if (pparent == NULL)
			_root = SubR;
		else if (pparent->_left == parent)
			pparent->_left = SubR;
		else
			pparent->_right = SubR;
		//4.重新链上SubRL结点
		if (SubRL != NULL)
			SubRL->_parent = parent;
		
	}

	void _RotateR(Node* &parent)
	{
		//1.将要修改的结点标记起来
		Node* SubL = parent->_left;
		Node* SubLR = SubL->_right;
		Node* pparent = parent->_parent;
		//2.重新链上SubL结点
		SubL->_right = parent;
		SubL->_parent = parent->_parent;
		SubL->_bf = 0;
		//3.重新链上parent结点
		parent->_left = SubLR;
		parent->_parent = SubL;
		parent->_bf = 0;
		//4.改变pparent的指向结点
		if (pparent == NULL)
			_root = SubL;
		else if (pparent->_left == parent)
			pparent->_left = SubL;
		else
			pparent->_right = SubL;
		//5.重新链上SubRL结点
		if (SubLR != NULL)
			SubLR->_parent = parent;
	}

	void _RotateLR(Node* &parent)
	{
		//双旋的时候在某些情况下会导致bf发生异常
		Node* SubL = parent->_left;
		Node* SubLR = SubL->_right;
		int bf = SubLR->_bf;
		_RotateL(parent->_left);
		_RotateR(parent);
		if (bf == -1)
		{
			parent->_bf = 1;
			SubL->_bf = 0;
		}
		else if (bf == 1)
		{
			parent->_bf = 0;
			SubL->_bf = -1;
		}
		else
		{
			SubL->_bf = parent->_bf = 0;
		}
		SubLR->_bf = 0;
	}

	void _RotateRL(Node* &parent)
	{
		Node* SubR = parent->_right;
		Node* SubRL = SubR->_left;
		int bf = SubRL->_bf;
		_RotateR(parent->_right);
		_RotateL(parent);
		if (bf == 1)
		{
			parent->_bf = -1;
			SubR->_bf = 0;
		}
		else if (bf == -1)
		{
			parent->_bf = 0;
			SubR->_bf = 1;
		}
		else
		{
			SubR->_bf = parent->_bf = 0;
		}
		SubRL->_bf = 0;
	}