以下图的平衡因子统一为左子树高度减去右子树高度。

1 左单旋 （右右 – 在较高右子树的右侧插入节点）

附上：单个节点声明的代码

struct AVLTreeNode
{
	AVLTreeNode(const K& key, const V& value)
	: _pLeft(NULL)
	, _pRight(NULL)
	, _pParent(NULL)
	, _key(key)
	, _value(value)
	, _bf(0)
	{}


	AVLTreeNode<K, V> *_pLeft;
	AVLTreeNode<K, V> *_pRight;
	AVLTreeNode<K, V> *_pParent;
	K _key;
	V _value;
	int _bf;       // 平衡因子：right-left
};

附上 – 左单旋代码：

void _RotateL(Node* pParent)
	{
		if (pParent)
		{
			Node *pPParent = pParent->_pParent;
			Node * pSubR = pParent->_pRight;
			Node * pSubRL = pParent->_pLeft;
			if (pSubRL)
			{
				pSubRL->_pParent = pParent;
			}
			pParent->_pRight = pSubRL;
			pSubR->_pLeft = pParent;
			pParent->_pParent = pSubR;
			pSubR->_pParent = pPParent;
			if (pPParent == NULL)
			{
				_pRoot = pSubR;
			}
			else
			{
				if (pPParent->_pLeft == pParent) pPParent->_pLeft = pSubR;
				else
					pPParent->_pRight = pSubR;
			}
			pSubR->_bf = 0;
			pParent->_bf = 0;
		}
	}

2 右单旋 （左左-在较高左子树中的左侧插入节点）

附上 -右单旋代码：

void _RotateR(Node* pParent)
	{
		if (pParent)
		{
			Node*pPParent = pParent->_pParent;
			Node*pSubL = pParent->_pLeft;
			Node*pSubLR = pSubL->_pRight;
			if (pSubLR)
			{
				pSubLR->_pParent = pParent;
			}
			pParent->_pLeft = pSubLR;
			pParent->_pParent = pSubL;
			pSubL->_pRight = pParent;
			pSubL->_pParent = pPParent;  
			if (pPParent==NULL)
			{
				_pRoot = pSubL;
			}
			else
			{
				if (pParent->_pRight == pParent)pParent->_pRight = pSubL;
				else
					pParent->_pLeft = pSubL;
			}
			pSubL->_bf = 0;
			pParent->_bf = 0;

		}
	}

3 右左双旋（右左-在较高右子树的左侧插入）

附上代码 – 右左双旋：

void _RotateRL(Node* pParent)
	{
		Node *PsubR = pParent->_pRight;
		Node* pSubRL = PsubR->_pLeft;
		int bf = pSubRL->_bf;
		_RotateR(pParent->_pRight);
		_Rotate(pParent);
		if (bf == -1) pParent->_bf = 1;
		else PsubR->_bf = -1;
	}

4 左右双旋（左右-在较高左子树的右侧插入）

void _RotateLR(Node* pParent)
	{
		Node * PsubL = pParent->_pLeft;
		Node * psubLR = PsubL->_pRight;
		int bf = psubLR->_bf;
		_RotateL(pParent->_pLeft);
		_RotateR(pParent);
		if (bf == 1) pParent->_bf = -1;
		else PsubL->_bf = 1;
	}