AVL树的旋转、插入、 详解

AVL树或者空树，或者它的左右子树的高度之差的绝对值不超过1；详情的平衡因子请看小编上篇博客。

AVL的平衡旋转可是转晕了不少同学啊，其实理清思路还是很简单的，那么小雷同学就开始show time！

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什么时候旋转？怎么旋转？

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左单旋：

template
void AVLTree::RotateL (AVLNode *&ptr)
{
	AVLNode *subL =ptr;
	ptr =subL->right;
	subL->right = ptr->left;
	ptr->left = subL;
	ptr->bf = subL->bf = 0;
};

/********************************************************************************************************************/

先左后右旋转

template
void AVLTree::RotateLR (AVLNode*&ptr)
{
	AVLNode *subR =ptr,*subL = subR->left;
	ptr = subL->right;
	subL->right = ptr->left;
	ptr->left = subL;
	if(ptr->bf<= 0)subL->bf = 0;
	else
		subL->bf = -1;


	subR ->left = ptr- >right;
	if(ptr->bf == -1)subR->bf = 1;
	else subR->bf = 0;
	ptr->bf = 0;
	ptr->right = subR;
};

////////////////////////************************************************************/

插入

template
bool AVLTree::Insert(AVLNode*&ptr,E&el)
{
	AVLNode *pr = NULL; *p = ptr,*q; int d;
	stack*>st;
	while(p != NULL)
	{
		if(el == p->data) return false;
		pr = p;st.push(pr);
		if(el < p->data) p = p->left;
		else p = p->right;
	}
	p = new AVLNode(el);
	if(p == NULL){cout<<"error";}
	if(pr == NULL){ptr = p;return true;}
	else pr->right = p;
	while (st.IsEmpty() == false)
	{
		st.pop(pr);
		 if(p == pr->left)
			 pr->bf--;
		 else
			 pr->bf++;
		 if(pr->bf == 0)break;
		 if(pr->bf == 1|| pr->bf == -1)
			 p =pr;
		 else
		 {
			 d = (pr->bf<0)>-1:1;
			 if(p->bf == d)
			 {
				 if(d == -1)RotateR(pr);
				 else RotateL(pr);
			 }
			 else
			 {
				 if(d == -1)RotateLR(pr);
				 else RotateRL(pr);
			 }
			 break;
		 }
		 if(st.IsEmpty() == true) ptr = pr;
		 else
		 {
			 st.getTop(q);
			 if(q ->data > pr->data)q->left = pr;
			 else q->right = pr;
		 }
		 return true;
	}
}