【PAT】1066. Root of AVL Tree

考查点：AVL，插入

思路：只要会写AVL即可

#define LOCAL
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#define FOR(i, x, y) for(int i = x; i < y; i++)
#define rFOR(i, x, y) for(int i = x; i > = y; i--)
#define MAXN 110
#define oo 0x3f3f3f3f
using namespace std;
int data[MAXN];
struct node{
int v,height;
node *lchild,*rchild;
};
node* newNode(int v)
{
node* Node=new node;
Node->v=v;
Node->height=1;
Node->lchild=Node->rchild=NULL;
return Node;
}
int getHeight(node* root)
{
if(root==NULL) return 0;
return root->height;
}
int getBalanceFactor(node* root)
{
return getHeight(root->lchild)-getHeight(root->rchild);
}
void updateHeight(node* root)
{
root->height=max(getHeight(root->lchild),getHeight(root->rchild))+1;
}

void searchAVL(node* root,int x)
{
if(root==NULL) {
printf("search failed\n");
return;
}
if(x==root->v){
printf("%d\n",root->v);
}else if(x<root->v) searchAVL(root->lchild,x);
else searchAVL(root->rchild,x);
}

void LR(node* &root)
{
node* temp=root->rchild;
root->rchild=temp->lchild;
temp->lchild=root;
updateHeight(root);
updateHeight(temp);
root=temp;
}

void RR(node* &root)
{
node* temp=root->lchild;
root->lchild=temp->rchild;
temp->rchild=root;
updateHeight(root);
updateHeight(temp);
root=temp;
}
void insertAVL(node* &root,int v)
{
if(root==NULL){
root=newNode(v);
return;
}
if(v<root->v){
insertAVL(root->lchild,v);
updateHeight(root);
if(getBalanceFactor(root)==2){
if(getBalanceFactor(root->lchild)==1){
RR(root);
}else if(getBalanceFactor(root->lchild)==-1){
LR(root->lchild);
RR(root);
}
}
}else{
insertAVL(root->rchild,v);
updateHeight(root);
if(getBalanceFactor(root)==-2){
if(getBalanceFactor(root->rchild)==-1){
LR(root);
}else if(getBalanceFactor(root->rchild)==1){
RR(root->rchild);
LR(root);
}
}
}
}
node* Create(int data[],int n)
{
node* root=NULL;
FOR(i,0,n)
{
insertAVL(root,data[i]);
}
return root;
}
int main()
{
#ifdef LOCAL
freopen("data.in","r",stdin);
freopen("data.out","w",stdout);
#endif // LOCAL
int n;
scanf("%d",&n);
FOR(i,0,n)
{
scanf("%d",&data[i]);
}
node* root=Create(data,n);
printf("%d",root->v);

return 0;
}