1652: [Usaco2006 Feb]Treats for the Cows (区间DP)

#include<iostream>
#include<cstdio>
using namespace std;
int n,a[2005],f[2005][2005];
void dp(int i,int j){
if(i==j){f[i][i]=a[i]*n;return;}
if(!f[i+1][j])dp(i+1,j);
if(!f[i][j-1])dp(i,j-1);
f[i][j]=max(f[i][j],f[i+1][j]+a[i]*(n-j+i));
f[i][j]=max(f[i][j],f[i][j-1]+a[j]*(n-j+i));
}
int main(){
scanf("%d",&n);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]);
dp(1,n);
printf("%d",f[1]
);
return 0;
}