PAT甲级 1066 - Root of AVL Tree

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AVL左旋和右旋操作：

1. LL时，需要进行右旋
2. RR时，需要进行左旋
3. LR时，先左旋再右旋
4. RL时，先右旋再左旋

所以判断当前状态后，只需左右旋两个基本操作。这两个基本操作，需要参考一个比较的不平衡树来写代码。

#include<bits/stdc++.h>
using namespace std;
struct node{
    node *l,*r;
    int v;
};
node *rotateLeft(node *rt){
    node *temp = rt->r;
    rt->r = temp->l; 
    temp->l = rt;
    return temp;
}
node *rotateRight(){
    node *temp = rt->l;
    rt->l = temp->r; 
    temp->r = rt;
    return temp;
}
node *RR(node *rt){  //rotate left
    return rotateLeft(rt);
}
node *LL(node *rt){ //rotate right
    return rotateRight(rt);
}
node *RL(node *rt){
    rt->r = rotateRight(rt->r); //rotate right
    return rotateLeft(rt);      //rotate left
}
node *LR(node *rt){
    rt->l = rotateLeft(rt->l);  //rotate left
    return rotateRight(rt);         //rotate right
}
int getHeight(node *rt){
    if(rt==NULL)return 0;
    return max(getHeight(rt->l),getHeight(rt->r))+1;
}

node *insert(node *rt,int v){
    if(rt == NULL){
        rt = new node();
        rt->l=NULL;
        rt->r=NULL;
        rt->v=v;
        return rt;   //tmp
    }
    if(rt->v > v){
        rt->l = insert(rt->l,v);
        if(abs(getHeight(rt->r)-getHeight(rt->l))==2){
            if(rt->l->v > v){
                rt=LL(rt);
            }else{
                rt=LR(rt);
            }
        }
    }else{
        rt->r = insert(rt->r,v);
        if(abs(getHeight(rt->r)-getHeight(rt->l))==2){
            if(rt->r->v > v){
                rt=RL(rt);
            }else{
                rt=RR(rt);
            }
        }
    }
    return rt;
}

int main(){
    int n,tmp;
    scanf("%d",&n);
    node *tree=NULL;//init
    for(int i=0;i<n;++i){
        scanf("%d",&tmp);
        tree=insert(tree,tmp);
    }   
    printf("%d",tree->v);
    return 0;
}