BZOJ4753: [Jsoi2016]最佳团体

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int MAXN=1e6+10,INF=1e4+10;
inline char nc()
{
    static char buf[MAXN],*p1=buf,*p2=buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,MAXN,stdin),p1==p2)?EOF:*p1++;
}
inline int read()
{
    char c=nc();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=nc();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=nc();}
    return x*f;
}
int N,K;
int S[MAXN],P[MAXN],R[MAXN];
struct node
{
    int u,v,nxt;
}edge[MAXN];
int head[MAXN];
int num=1;
inline void AddEdge(int x,int y)
{
    edge[num].u=x;
    edge[num].v=y;
    edge[num].nxt=head[x];
    head[x]=num++;
}
double dp[2501][2501],/*i处，选了j个*/siz[MAXN],w[MAXN];
void find(int now)
{
    siz[now]=1;
    for(int i=head[now];i!=-1;i=edge[i].nxt)
        find(edge[i].v),siz[now]+=siz[edge[i].v];
}
void dfs(int now)
{
    int tot=0,b=0;
    if(now) dp[now][1]=w[now],tot=1,b++;
    else dp[now][0]=0;
    for(int i=head[now];i!=-1;i=edge[i].nxt)
    {
        dfs(edge[i].v);
        for(int j=tot;j>=b;j--)//背包容量 
            for(int k=1;k<=siz[edge[i].v];k++)
                dp[now][j+k]=max(dp[now][j+k],dp[now][j]+dp[edge[i].v][k]);
        tot+=siz[edge[i].v];//必须在后面加 
    }
}
bool check(double val)
{
    memset(dp,0xc2,sizeof(dp));
    for(int i=1;i<=N;i++) w[i]=P[i]-val*S[i];
    dfs(0);
    return dp[0][K]>=0;
}
int main()
{
    #ifdef WIN32
    freopen("a.in","r",stdin);
    #else 
    #endif
    memset(head,-1,sizeof(head));
    K=read(),N=read();
    for(int i=1;i<=N;i++)
    {
        S[i]=read(),P[i]=read(),R[i]=read();
        AddEdge(R[i],i);
    }
    find(0);
    double l=0,r=INF;
    double ans=0;
    while(r-l>1e-5)
    {
        double mid=(l+r)/2;
        if(check(mid)) l=mid;
        else r=mid;    
    }
    printf("%.3lf",(l+r)/2);
     return 0;
}