敲这个题时，预备知识是知道四种旋转方式，分别是LL、RR、LR、RL，对应每一种的变换方式要做到会旋转，会写关键的代码

这个题是参照一篇博客写的，然后自己又理解了一遍。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct node
{
    struct node *l, *r;
    int data, d;
};
int max(int a,int b)
{
    if(a < b)
        return b;
    else return a;
}
int deep(struct node *root)
{
    if(root == NULL)
        return -1;
    else return root->d;
}
struct node *LL(struct node *root)
{
    struct node *p;
    p = root->l;
    root->l = p->r;
    p->r = root;
    root->d = max(deep(root->l), deep(root->r)) + 1;
    return p;
};
struct node *RR(struct node *root)
{
    struct node *p;
    p = root->r;
    root->r = p->l;
    p->l = root;
    root->d = max(deep(root->l),deep(root->r)) + 1;
    return p;
};
struct node *LR(struct node *root)
{
    /*//如果用以下代码的话会出现超时的错误，因为如果树越来越庞大的时候
        每次都是这样处理数据就会很麻烦，也很耗时。要用RR和LL时的结果。
    struct node *p;
    p = root->l;
    root->l = p->r->r;
    p->r = p->r->l;
    p->r->l = p;
    p->r->r = root;
    root->d = max(deep(root->l),deep(root->r)) + 1;
    return p;*/
    root->l = RR(root->l);
    root = LL(root);
    return root;
};
struct node *RL(struct node *root)
{
    /*struct node *p;
    p = root->r;
    p->l = p->l->r;
    root->r = p->l->l;
    p->l->r = p;
    p->l->l = root;
    root->d = max(deep(root->l),deep(root->r)) + 1;
    return p;*/
    root->r = LL(root->r);
    root = RR(root);
    return root;
};
struct node *creat(int x,struct node *root)
{
    if(root == NULL)
    {
        root = (struct node *)malloc(sizeof(struct node));
        root->data = x;
        root->d = 0;
        root->l = NULL;
        root->r = NULL;
    }
    else
    {
        if(x < root->data)
        {
            root->l = creat(x,root->l);
            if(deep(root->l) - deep(root->r) > 1)
            {
                 if(x < root->l->data)
                    root = LL(root);
                 else root = LR(root);
            }
        }
        else if(x > root->data)
        {
            root->r = creat(x,root->r);
            if(deep(root->r) - deep(root->l) > 1)
            {
                if(x > root->r->data)
                    root = RR(root);
                else root = RL(root);
            }
        }
    }
     root->d = max(deep(root->l),deep(root->r)) + 1;
     return root;
};
int main()
{
    struct node *root;
   int n, i,x;
   scanf("%d",&n);
   root = NULL;
   for(i = 0;i < n;i++)
   {
       scanf("%d",&x);
       root = creat(x,root);
   }
   printf("%d\n",root->data);
    return 0;
}