1066 Root of AVL Tree 需再做

Posted 2021-09-04 CSU迦叶

1. 这题如果不知道平衡二叉树怎么平衡的(左旋右旋那一套)应该不可能做出吧，那就输出中位数回点血了。

2. 需要具备的基础知识：怎么将结点插入平衡二叉树。

3. 我犯的一个错误：把更新高度的函数直接返回了高度，而不没有修改高度。

AC代码

#include<cstdio>
#include<map>
#include<set>
#include<string>
#include<cstring>
#include<iostream>
#include<vector>
#include<stack>
#include<queue>
#include<algorithm>
#include<cmath>
typedef long long LL;

using namespace std;

const int maxn = 30;

struct Node{
	int data,hei;
	Node *lchild,*rchild;
};

Node* newNode(int v){
	Node* root = new Node;
	root->data = v;
	root->hei = 1;
	root->lchild=root->rchild=NULL;
	return root;
}

int getHei(Node* root){
	if(root==NULL)return 0;
	else return root->hei;
}

void updateHei(Node* root){
	root->hei =  max(getHei(root->lchild),getHei(root->rchild))+1;
}

int getBF(Node* root){
	return getHei(root->lchild)-getHei(root->rchild);
}

void R(Node* &root){
	 Node* temp = root->lchild;
	 root->lchild = temp->rchild;
	 temp->rchild = root;
	 updateHei(root);
	 updateHei(temp);
	 root = temp;
}

void L(Node* &root){
	Node* temp = root->rchild;
	root->rchild = temp->lchild;
	temp->lchild = root;
	updateHei(root);
	updateHei(temp);
	root = temp;
}

void insert(Node* &root,int v){
	if(root==NULL){
		root = newNode(v);
		return;
	}
	
	if(v<root->data){//插入左子树
		insert(root->lchild,v);
		updateHei(root);
		if(getBF(root)==2){//正向失衡 
			if(getBF(root->lchild)==1){//LL
				R(root);
			}else{//LR
				L(root->lchild);
				R(root);
			}
		} 
	}else{
		insert(root->rchild,v);
		updateHei(root);
		if(getBF(root)==-2){//反向失衡 
			if(getBF(root->rchild)==-1){//RR
				L(root);
			}else{//RL
				R(root->rchild);
				L(root);
			} 
		}
	}
}

Node* createTree(int data[30],int n){
	Node* root = NULL;
	for(int i=0;i<n;i++)insert(root,data[i]);
	return root;
}

int main(){
	int data[maxn],n;
	scanf("%d",&n);
	for(int i=0;i<n;i++)scanf("%d",&data[i]);
	Node* root = createTree(data,n);
	printf("%d",root->data);
	return 0;
}