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[];
 int f[][];
 int Max;
 int ans;
 void in(int &x)
 {
     int y=;
     char c=g();x=;
     while(c<''||c>'')
     {
     if(c=='-')
     y=-;
     c=g();
     }
     while(c<=''&&c>='')x=x*+c-'',c=g();
     x*=y;
 }
 void o(int x)
 {
     if(x<)
     {
         p('-');
         x=-x;
     }
     if(x>)o(x/);
     p(x%+'');
 }
 int main()
 {
          in(m);
          For(jj,,m)
          in(a[jj]);
          For(i,,m)
          f[i][i]=m*a[i];
        For(l,,m-)
           For(i,,m-l)
               f[i][i+l]=max(f[i+][i+l]+a[i]*(m-l),f[i][i+l-]+a[i+l]*(m-l));
      o(f[][m]);
      return ;
 }