P2858 [USACO06FEB]奶牛零食Treats for the Cows

P2858 [USACO06FEB]奶牛零食Treats for the Cows
区间dp，级像矩阵取数，
f[i][i+l]=max(f[i+1][i+l]+a[i]*(m-l),f[i][i+l-1]+a[i+l]*(m-l));

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<cstring>
#define inf 2147483647
#define For(i,a,b) for(register int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()
//by war
//2017.10.19
using namespace std;
int n,m;
int a[2010];
int f[2010][2010];
int Max;
int ans;
void in(int &x)
{
    int y=1;
    char c=g();x=0;
    while(c<'0'||c>'9')
    {
    if(c=='-')
    y=-1;
    c=g();
    }
    while(c<='9'&&c>='0')x=x*10+c-'0',c=g();
    x*=y;
}
void o(int x)
{
    if(x<0)
    {
        p('-');
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+'0');
}
int main()
{
         in(m);
         For(jj,1,m)
         in(a[jj]);
         For(i,1,m)
         f[i][i]=m*a[i];
       For(l,1,m-1)
          For(i,1,m-l)
              f[i][i+l]=max(f[i+1][i+l]+a[i]*(m-l),f[i][i+l-1]+a[i+l]*(m-l));
     o(f[1][m]);
     return 0;
}