学步园

题目：http://pat.zju.edu.cn/contests/pat-a-practise/1066

题解：

考察数据结构;AVL树。

重点就是四种情况的识别和处理。

代码：

#include<cstdio>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<algorithm>
using namespace std;
#define INF 0x6fffffff
#define MAX 25
struct point
{
    int value;
    int left;
    int right;
    int heigh;
}node[MAX];
int idx;
int getHeight(int root)
{
    if(root==-1) return -1;
    return node[root].heigh;
}
int rotateLL(int root)
{
    int child=node[root].left;
    node[root].left=node[child].right;//root的左孩纸变成原左孩纸的右孩纸
    node[child].right=root;//原root左孩纸的右孩纸变成root
    node[root].heigh=max(getHeight(node[root].left),getHeight(node[root].right))+1;
    node[child].heigh=max(getHeight(node[child].left),getHeight(node[child].right))+1;
    return child;
}
int rotateRR(int root)
{
    int child=node[root].right;
    node[root].right=node[child].left;//root的右孩纸变成原右孩纸的左孩纸
    node[child].left=root;//原root右孩纸的左孩纸变成root
    node[root].heigh=max(getHeight(node[root].left),getHeight(node[root].right))+1;
    node[child].heigh=max(getHeight(node[child].left),getHeight(node[child].right))+1;
    return child;
}
int rotateLR(int root)
{
    int child=node[root].left;
    node[root].left=rotateRR(child);
    return rotateLL(root);
}
int rotateRL(int root)
{
    int child=node[root].right;
    node[root].right=rotateLL(child);
    return rotateRR(root);
}
bool isBalance(int root)
{
    return abs(getHeight(node[root].left)-getHeight(node[root].right))<2;
}
int insertNode(int root,int x)//插入新结点
{
    if(root!=-1)
    {
        if(x>node[root].value)//右
        {
            node[root].right=insertNode(node[root].right,x);
            if(!isBalance(root))
            {
                if(x>node[node[root].right].value)//右右
                    root=rotateRR(root);
                else//右左
                    root=rotateRL(root);
            }
        }
        else
        {
            node[root].left=insertNode(node[root].left,x);
            if(!isBalance(root))
            {
                if(x>node[node[root].left].value)//左右
                    root=rotateLR(root);
                else//左左
                    root=rotateLL(root);
            }
        }
    }
    else
    {
        node[idx].value=x;
        node[idx].left=node[idx].right=-1;
        node[idx].heigh=0;
        root=idx;
        ++idx;
    }
    node[root].heigh=max(getHeight(node[root].left),getHeight(node[root].right))+1;
    return root;
}
void dfs(int root)
{
    if(root==-1) return;
    if(node[root].left!=-1)
    {
        printf("%d left-> %d\n",node[root].value,node[node[root].left].value);
        dfs(node[root].left);
    }
    if(node[root].right!=-1)
    {
        printf("%d right-> %d\n",node[root].value,node[node[root].right].value);
        dfs(node[root].right);
    }
}
int main()
{
    int n,x,root;
    scanf("%d",&n);
    idx=0;
    root=-1;
    for(int i=0;i<n;++i)
    {
        scanf("%d",&x);
        root=insertNode(root,x);
        //printf("start\n");//测试
        //dfs(root);
        //printf("\n");
    }
    //dfs(root);
    printf("%d\n",node[root].value);
    return 0;
}

来源：http://blog.csdn.net/acm_ted/article/details/20855913