HNOI 2002 营业额统计 入门Splay

题意：题意简单的说就是给一个数列，对于每一个数，用在它前面出现的数与它做差，找到对它来说最小的差，答案就是把每一个数的最小差相加。第一个数的最小差是它本身。

分析：这几天在练Splay（感觉自己太菜了），用splay来解决这个问题，维护一颗平衡树，然后依次插入，每次插入找到它的前驱和后继，得到每个数的贡献，最后相加算出答案。最最最简单的Splay应用，然而我还是调了很久的bug，不过没有照着板子抄还是有进步。这几天在网上看大佬写主席树，树链剖分，感觉自己真的太菜了。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define lch tr[x].ch[0]
#define rch tr[x].ch[1]
using namespace std;
const int N = 40000+5;
int n,rt, tot;
int a[N];
struct node
{
    int v,ch[2],fa,num;
    void set(int vv, int f)
    {
     v = vv, fa = f;
     ch[0] = ch[1]   = 0;
     num = 1;
    }
}tr[N];
void print()
{
    for(int x = 1; x <= n; x++)
    {
        cout <<tr[x].v <<"   ss  " <<tr[lch].v <<"      "<<tr[rch].v << endl;
    }
    cout <<"  -----------------------------" << endl;
}
void rotate(int x, int d)
{
    int y = tr[x].fa;
    tr[y].ch[!d] = tr[x].ch[d];
    tr[tr[x].ch[d]].fa = y;
    int z = tr[y].fa;
    if(z)
    {
      tr[z].ch[tr[z].ch[1] == y] =x;
    }
    tr[x].fa = z;
    tr[x].ch[d] = y;
    tr[y].fa = x;
}
void splay(int x, int to)
{
    while(tr[x].fa != to)
    {
        int y = tr[x].fa;
        if(tr[y].fa == to)
        {
            rotate(x,tr[y].ch[0] == x);
        }
        else
        {
            int z = tr[y].fa;
            int d = (tr[z].ch[0] == y);
            if(tr[y].ch[d] == x)
            {
                rotate(x,!d),rotate(x,d);
            }
            else
            {
                rotate(y,d); rotate(x,d);
            }
        }
    }
    if(to == 0) rt = x;
}
void insert(int v)
{
    if(rt == 0)
    {
        tr[rt = tot ++].set(v,0);
    }
    else
    {
        int x = rt, y = 0;
        while(x)
        {
           if(tr[x].v == v)
           {
               tr[x].num ++;
               break;
           }
           else if(v < tr[x].v) y = x, x = lch;
           else y = x, x = rch;
        }
        if(x == 0)
        {
            tr[y].ch[v < tr[y].v ? 0 : 1] = tot;
            x = tot;
            tr[tot++].set(v,y);
        }
        splay(x,0);
    }
}
int suc()
{
    int x = rt;
    if(rch)
    {
        x = rch;
        while(lch) x = lch;
        return tr[x].v;
    }
    else return -1;
}
int pre()
{
    int x = rt;
    if(lch)
    {
        x = lch;
        while(rch) x = rch;
        return tr[x].v;
    }
    else return -1;
}
int get()
{
    int x = rt;
    int ret = tr[x].v;
    if(tr[x].num > 1) return 0;
    int pr = pre(), su = suc();
    if(pr != -1 && su != -1)
    {
        int a = pr - tr[x].v; a = a > 0 ? a : -a;
        int b = su - tr[x].v; b= b > 0 ? b : -b;
        ret = min(a,b);
    }
    else if(pr != -1)
    {
         int a = pr - tr[x].v; a = a > 0 ? a : -a;
        ret = a;
    }
    else if(su != -1)
    {
          int b = su - tr[x].v; b= b > 0 ? b : -b;
          ret = b;
    }
    return ret;
}
int main()
{
    while(~scanf("%d",&n))
    {
        rt = 0; tot = 1;
        long long ans = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%d",&a[i]);
            insert(a[i]);
            ans += get();
        }
        printf("%lld\n",ans);
    }
}