luogu P2422 良好的感觉 单调队列dp

#include<map>
#include<queue>
#include<time.h>
#include<limits.h>
#include<cmath>
#include<ostream>
#include<iterator>
#include<set>
#include<stack>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define rep_1(i,m,n) for(int i=m;i<=n;i++)
#define mem(st) memset(st,0,sizeof st)
int read()
{
    int res=0,ch,flag=0;
    if((ch=getchar())=='-')             //判断正负
        flag=1;
    else if(ch>='0'&&ch<='9')           //得到完整的数
        res=ch-'0';
    while((ch=getchar())>='0'&&ch<='9')
        res=res*10+ch-'0';
    return flag?-res:res;
}
typedef long long ll;
typedef pair<int,int> pii;
typedef unsigned long long ull;
typedef pair<double,double> pdd;
const int inf = 0x3f3f3f3f;
const int N=1e6+10;
#define int long long
int a[N];
int sum[N];
int dp[N];
int q[N];
void solve()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
        sum[i]=sum[i-1]+a[i];
    }
    int hh=1,tt=1;
    for(int i=1;i<=n;i++)
    {
        while(hh<tt&&a[q[tt-1]]>a[i])
        {
            dp[q[tt-1]]+=sum[i-1]-sum[q[tt-1]];
            tt--;
        }
        dp[i]=sum[i]-sum[q[tt-1]];
        q[tt++]=i;
    }
    int ans=0;
    for(int i=1;i<=n;i++)
        ans=max(ans,a[i]*dp[i]);
    cout<<ans<<endl;
}
signed main()
{
    int t=1;
    while(t--)
        solve();
    return 0;
}