[HNOI2002]营业额统计

题目链接：传送门

题目大意：中文题，略

题目思路：Splay模板题，找前驱和后继

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <stack>
#include <cctype>
#include <queue>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <climits>
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid+1,r
#define fi first
#define se second
#define ping(x,y) ((x-y)*(x-y))
#define mst(x,y) memset(x,y,sizeof(x))
#define mcp(x,y) memcpy(x,y,sizeof(y))
using namespace std;
#define gamma 0.5772156649015328606065120
#define MOD 1000000007
#define inf 0x3f3f3f3f
#define N 100005
#define maxn 10
typedef pair<int,int> PII;
typedef long long LL;
LL read(){
    LL x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
    return x*f;
}

int n,m,cnt,num,ans;
struct Splay{
    int rt,sz;     ///根节点,树节点总数
    int va[N],son[N][2],fa[N];///值,左右儿子,父亲
    void spin(int t){     ///旋转操作
        int x=fa[t], f=fa[x], y=son[x][1]==t;
        son[x][y]=son[t][y^1], fa[son[x][y]]=x;
        son[t][y^1]=x, fa[x]=t, fa[t]=f;
        if(f) son[f][son[f][1]==x]=t;
    }
    void play(int x){     /// splay操作
        for(int i;i=fa[x];spin(x))
            if(fa[i])
            spin((x==son[i][0])==(i==son[fa[i]][0])?i:x);
        rt=x;
    }
    void ins(int v){///插入元素
        int y,x=rt;
        while(1){
            y=son[x][va[x]<v];
            if(!y){
                y=++sz, va[y]=v, fa[y]=x;
                son[y][0]=son[y][1]=0;
                son[x][va[x]<v]=y;
                break;
            }
            x=y;
        }play(y);
    }
    int suc(){    ///找后继
        int x=rt,y=son[x][1];
        while(son[y][0])y=son[y][0];
        return va[y];
    }
    int pre(){    ///找前驱
        int x=rt,y=son[x][0];
        while(son[y][1])y=son[y][1];
        return va[y];
    }
    void init(int x){  ///初始化,需要初始值
        sz=rt=1;va[rt]=x;
        fa[1]=son[1][0]=son[1][1]=0;
    }
}splay;

int main(){
    int i,j,group,x;
    n=read();
    if(scanf("%d",&x)==-1)x=0;
    ans=x;
    splay.init(inf);
    splay.ins(-inf);
    splay.ins(x);
    for(i=2;i<=n;++i){
        if(scanf("%d",&x)==-1)x=0;
        splay.ins(x);
        int t1=splay.pre(),t2=splay.suc();
        ans+=min(x-t1,t2-x);
    }
    printf("%d\n",ans);
    return 0;
}