[luoguP2858] [USACO06FEB]奶牛零食Treats for the Cows（DP）

 1 #include <cstdio>
 2 #include <iostream>
 3 
 4 const int MAXN = 2001;
 5 int n;
 6 int a[MAXN], f[MAXN][MAXN];
 7 
 8 inline int read()
 9 {
10     int x = 0, f = 1;
11     char ch = getchar();
12     for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
13     for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
14     return x * f;
15 }
16 
17 inline int max(int x, int y)
18 {
19     return x > y ? x : y;
20 }
21 
22 inline int dp(int x, int y)
23 {
24     if(f[x][y]) return f[x][y];
25     if(x == y) return f[x][y] = a[x] * n;
26     else return f[x][y] = max(dp(x + 1, y) + a[x] * (n - y + x), dp(x, y - 1) + a[y] * (n - y + x));
27 }
28 
29 int main()
30 {
31     int i;
32     n = read();
33     for(i = 1; i <= n; i++) a[i] = read();
34     printf("%d\n", dp(1, n));
35     return 0;                                                                                                                                                                                                                                                                                                                
36 }