|洛谷|NOIP2006|动态规划|P1063 能量项链

http://www.luogu.org/problem/show?pid=1063

类似于合并石子，只不过这里是环形的，只需要把a数组复制一遍，然后对[1..2n]区间进行DP，注意要逆推，答案是max{[1..n], [2..n+1], [3..n+2]....[n,n+n-1]}

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#define ms(i,j) memset(i,j, sizeof i);
using namespace std;
int a[300];
int n;
int f[300][300];
int main()
{
scanf("%d", &n);
for (int i=1;i<=n;i++)
{
scanf("%d", &a[i]);
a[i+n] = a[i];//环形
}
ms(f,0);
for (int i=2*n-1;i>0;i--)
for (int j=i+1;j<=2*n;j++)
for (int k=i;k<j;k++)
{
f[i][j] = max(f[i][j], f[i][k]+f[k+1][j]+a[i]*a[j+1]*a[k+1]);
}
int ans = 0;
for (int i=1;i<=n;i++)
ans = max(ans, f[i][i+n-1]);
printf("%d\n", ans);
return 0;
}