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));

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<queue>
 4 #include<algorithm>
 5 #include<cmath>
 6 #include<ctime>
 7 #include<cstring>
 8 #define inf 2147483647
 9 #define For(i,a,b) for(register int i=a;i<=b;i++)
10 #define p(a) putchar(a)
11 #define g() getchar()
12 //by war
13 //2017.10.19
14 using namespace std;
15 int n,m;
16 int a[2010];
17 int f[2010][2010];
18 int Max;
19 int ans;
20 void in(int &x)
21 {
22     int y=1;
23     char c=g();x=0;
24     while(c<'0'||c>'9')
25     {
26     if(c=='-')
27     y=-1;
28     c=g();
29     }
30     while(c<='9'&&c>='0')x=x*10+c-'0',c=g();
31     x*=y;
32 }
33 void o(int x)
34 {
35     if(x<0)
36     {
37         p('-');
38         x=-x;
39     }
40     if(x>9)o(x/10);
41     p(x%10+'0');
42 }
43 int main()
44 {
45          in(m);
46          For(jj,1,m)
47          in(a[jj]);
48          For(i,1,m)
49          f[i][i]=m*a[i];
50        For(l,1,m-1)
51           For(i,1,m-l)
52               f[i][i+l]=max(f[i+1][i+l]+a[i]*(m-l),f[i][i+l-1]+a[i+l]*(m-l));
53      o(f[1][m]);
54      return 0;
55 }

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