bzoj千题计划184：bzoj1261: [SCOI2006]zh_tree

#include<cstdio>
#include<algorithm>

using namespace std;

double k,c;

int a[31];
double f[31];

double dp[31][31][31];
bool vis[31][31][31];

double dfs(int l,int r,int dep)
{
    if(l>r) return 0;
    if(vis[l][r][dep]) return dp[l][r][dep];
    vis[l][r][dep]=true;
    dp[l][r][dep]=1e9;
    for(int i=l;i<=r;++i)
        dp[l][r][dep]=min(dp[l][r][dep],dfs(l,i-1,dep+1)+dfs(i+1,r,dep+1)+(k*(dep+1)+c)*f[i]);
    return dp[l][r][dep];
}

int main()
{
    int n;
    scanf("%d%lf%lf",&n,&k,&c);
    int m=0;
    for(int i=1;i<=n;++i) scanf("%d",&a[i]),m+=a[i];
    for(int i=1;i<=n;++i) f[i]=1.0*a[i]/m;
    printf("%.3lf",dfs(1,n,0));
}