1066. Root of AVL Tree

最新推荐文章于 2019-01-22 17:29:00 发布

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最新推荐文章于 2019-01-22 17:29:00 发布

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分类专栏： PAT 文章标签： PAT C++

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1066. Root of AVL Tree (25)

时间限制

100 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.

Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=20) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print ythe root of the resulting AVL tree in one line.

Sample Input 1:

5
88 70 61 96 120

Sample Output 1:

Sample Input 2:

7
88 70 61 96 120 90 65

Sample Output 2:

我服了。。。我把自己写的和网上的对比了N久，基本改成一样的，也没发现哪里错了。

第一组样例就不行，提交有一组答案不对。

心态爆炸，不找了。

这题学到了一个点，AVL 的RL和LR操作可以先在子树上进行L/R再在自身上进行R/L。

#include<iostream>

using namespace std;

typedef struct node
{
	int v,h;
	node* l;
	node* r;
};

int H(node* root)
{
	if(root==NULL)
		return -1;
	return root->h;
}
node * LL(node* root)
{
	node* tmp=root->l;
	root->l=tmp->r;
	tmp->r=root;
	root->h==max(H(root->l),H(root->r))+1;
	tmp->h==max(H(tmp->l),H(tmp->r))+1;
	return tmp;	
}
node * RR(node* root)
{
	node* tmp=root->r;
	root->r=tmp->l;
	tmp->l=root;
	root->h==max(H(root->l),H(root->r))+1;
	tmp->h==max(H(tmp->l),H(tmp->r))+1;
	return tmp;
}
node * LR(node* root)
{
	node* tmp=root->l;
	root->l=RR(tmp);
	return LL(root);
}
node * RL(node* root)
{
	node* tmp=root->r;
	root->r=LL(tmp);
	return RR(root);
}
bool Isbalance(node* root)
{
	return abs(H(root->l)-H(root->r))<2;
}

node* Insert(node* root,int num)
{
	if(root==NULL)
	{
		root=new node;
		root->v=num;
		root->h=0;
		root->l=root->r=NULL;
	}
	else
	{
		if(num<root->v)
		{
			root->l=Insert(root->l,num);
			if(!Isbalance(root))
			{
				if(num<root->l->v)
					root=LL(root);
				else
					root=LR(root);
			}
		}
		else
		{
			root->r=Insert(root->r,num);
			if(!Isbalance(root))
			{
				if(num>root->r->v)
					root=RR(root);
				else
					root=RL(root);
			}
		}
	}
	root->h=max(H(root->l),H(root->r))+1;
	return root;
}
int main()
{
	int n;
	cin>>n;
	node* root=NULL;
	for(int i=0;i<n;++i)
	{
		int num;
		cin>>num;
		root=Insert(root,num);
	}
	cout<<root->v<<endl;
	return 0;
}