luoguP2422 良好的感觉

定义A=在a[i]~a[j]中最小值乘以总和，输出最大的A

#include<bits/stdc++.h>

using namespace std;

#define MAXN 100010

typedef long long ll;

int n;
ll a[MAXN];
ll sum[MAXN];
ll f[MAXN],t[MAXN];
int tail,head;

int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%lld",&a[i]),sum[i]=sum[i-1]+a[i];
    a[n+1]=0;
    for(int i=1;i<=n+1;i++)
    {
        while(a[t[tail]]>a[i])
        {
            f[t[tail]]+=sum[i-1]-sum[t[tail]];
            tail--;
        }
        f[i]+=sum[i]-sum[t[tail]];
        tail++;t[tail]=i;
    }
    ll ans=0;
    for(int i=1;i<=n;i++) ans=max(ans,a[i]*f[i]);
    cout<<ans<<endl;
}