BZOJ 1588: [HNOI2002]营业额统计 双向链表

//qscqesze
#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <set>
#include <vector>
#include <sstream>
#include <queue>
#include <typeinfo>
#include <fstream>
#include <map>
typedef long long ll;
using namespace std;
//freopen("D.in","r",stdin);
//freopen("D.out","w",stdout);
#define sspeed ios_base::sync_with_stdio(0);cin.tie(0)
#define maxn 400001
#define mod 10007
#define eps 1e-9
//const int inf=0x7fffffff;   //无限大
const int inf=0x3f3f3f3f;
/*

*/
//**************************************************************************************

struct node
{
    int p,v,left,right;
}a[maxn];

int n,ra[maxn];
inline bool cmp(node a,node b)
{
    return a.v<b.v;
}
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i].v;
        a[i].p=i;
    }
    sort(a+1,a+n+1,cmp);
    for(int i=1;i<=n;i++)
    {
        ra[a[i].p]=i;
        a[i].left=i-1;
        a[i].right=i+1;
    }
    a[n].right=0;
    int ans=a[ra[1]].v;
    for(int i=n;i>1;i--)
    {

        int x=ra[i];
        if(a[x].left!=0&&a[x].right!=0)
        {

            ans+=min(a[x].v-a[a[x].left].v,a[a[x].right].v-a[x].v);
            a[a[x].left].right=a[x].right;
            a[a[x].right].left=a[x].left;
        }
        else if(a[x].left==0)
        {

            ans+=a[a[x].right].v-a[x].v;
            a[a[x].right].left=0;
        }
        else
        {
            ans+=a[x].v-a[a[x].left].v;
            a[a[x].left].right=0;
        }

    }
    cout<<ans<<endl;
    return 0;
}