【luogu2858】 [USACO06FEB]奶牛零食Treats for the Cows [动态规划 区间dp]

P2858 [USACO06FEB]奶牛零食Treats for the Cows

我们可以从最后往外推 当前状态就只由上一个状态决定

就是合唱队那道题改一下

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<cmath>
#include<stack>
#include<algorithm>
using namespace std;
#define ll long long
#define rg register
const int N=2000+5,inf=0x3f3f3f3f,P=19650827;
int n,a[N],f[N][N];
template <class t>void rd(t &x)
{
    x=0;int w=0;char ch=0;
    while(!isdigit(ch)) w|=ch=='-',ch=getchar();
    while(isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    x=w?-x:x;
}

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("nocows.out","w",stdout);
    rd(n);
    for(rg int i=1;i<=n;++i) rd(a[i]),f[i][i]=a[i]*n;
    for(rg int i=2;i<=n;++i)
    {
        for(rg int l=1;l<n&&l+i-1<=n;++l)
        {
            int r=l+i-1;
            f[l][r]=max(f[l+1][r]+a[l]*(n-i+1),f[l][r-1]+a[r]*(n-i+1));
        }
    }
    printf("%d",f[1][n]);
    return 0;
}