P1642 规划

Posted 2020-08-10 tcswuzb

题目链接

题意分析

一看就知道是一道\(01\)分数规划的题

我们二分值之后 跑树形背包就可以了

CODE:

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdlib>
#include<string>
#include<queue>
#include<map>
#include<stack>
#include<list>
#include<set>
#include<deque>
#include<vector>
#include<ctime>
#define ll long long
#define inf 1e9
#define N 508
#define IL inline
#define M 1008611
#define D double
#define eps 1e-5
#define R register
using namespace std;
template<typename T>IL void read(T &_)
{
    T __=0,___=1;char ____=getchar();
    while(!isdigit(____)) {if(____=='-') ___=0;____=getchar();}
    while(isdigit(____)) {__=(__<<1)+(__<<3)+____-'0';____=getchar();}
    _=___ ? __:-__;
}
/*-------------OI使我快乐-------------*/
int n,m,tot;
struct Node
{
    int xx,yy;
}e[N];
D dp[N][N],num[N];
D le,ri=inf,ans;
int siz[N],to[N],nex[N],head[N];
IL void add(int x,int y)
{to[++tot]=y;nex[tot]=head[x];head[x]=tot;}
IL void dfs(int now,int fat)
{
    dp[now][0]=0;siz[now]=1;
    for(R int i=head[now];i;i=nex[i])
    {
        int v=to[i];
        if(v==fat) continue;
        dfs(v,now);
        siz[now]+=siz[v];
        for(R int j=min(m,siz[now]);j>=0;--j)
         for(R int k=0;k<=min(j,siz[v]);++k)
          dp[now][j]=max(dp[now][j],dp[now][j-k]+dp[v][k]);
    }
    for(R int i=siz[now];i;--i) dp[now][i]=dp[now][i-1]+num[now];
}
IL bool check(D now)
{
    for(R int i=1;i<=n;++i)
     for(R int j=0;j<=m;++j) dp[i][j]=-inf;
    for(R int i=1;i<=n;++i) num[i]=(D)e[i].xx-((D)now*e[i].yy); 
    dfs(1,0);
    for(R int i=1;i<=n;++i)
    if(dp[i][m]>-eps) return 1;
    return 0;
}
int main()
{
//  freopen(".in","r",stdin);
//  freopen(".out","w",stdout);
    read(n);read(m);m=n-m;
    for(R int i=1;i<=n;++i) read(e[i].xx);
    for(R int i=1;i<=n;++i) read(e[i].yy);
    for(R int i=1,x,y;i<n;++i)
    {
        read(x);read(y);
        add(x,y);add(y,x);
    }
    while((ri-le)>eps)
    {
        D mid=(le+ri)/2.0;
        if(check(mid)) ans=le=mid;
        else ri=mid;
    }
    printf("%.1f\n",ans);
//  fclose(stdin);
//  fclose(stdout);
    return 0;
}

HEOI 2019 RP++