bzoj1652 / P2858 [USACO06FEB]奶牛零食Treats for the Cows

P2858 [USACO06FEB]奶牛零食Treats for the Cows

区间dp

设$f[l][r]$为取区间$[l,r]$的最优解，蓝后倒着推

$f[l][r]=max(f[l+1][r]+a[l]*p,f[l][r-1]+a[r]*p)$

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 using namespace std;
 int max(int a,int b){return a>b?a:b;}
 #define N 2010
 int a[N],f[N][N],n;
 int main(){
     //freopen("P2858.in","r",stdin);
     scanf("%d",&n);
     for(int i=;i<=n;++i)
         scanf("%d",&a[i]),f[i][i]=a[i]*n;
     for(int i=;i<=n;++i)
         for(int l=,r,p;l+i-<=n;++l){
             r=l+i-; p=n-i+;
             f[l][r]=max(f[l+][r]+a[l]*p,f[l][r-]+a[r]*p);
         }
     printf("%d",f[][n]);
     return ;
 }