luoguP1084 疫情控制(题解)(搜索+贪心)

luoguP1084 疫情控制 题目

#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define il inline
#define rg register
#define ll long long
#define N 60000
#define inf 2147483647
using namespace std;

int n,m,hd[N],cnt,u,v,w;
int c,idx[N];
int le,ri=;
int dis[N][],up[N][];
int ok[N],use[N],vis[N];
struct S{
    int res,idx;
}ne[N],to[N];
struct T{
    int nt,to,w;
}edge[N<<];
il void re(rg int &x);
void add(rg int fm,rg int to,rg int w);
void ST(rg int i,rg int fa);
int check(rg int lim);
int Dfs(rg int u,rg int fa);
int Cmp(const S &x,const S &y);

int main()
{
    re(n);
    for(rg int i=;i<n;++i)
    {
        re(u),re(v),re(w);
        add(u,v,w),add(v,u,w);
        if(u==||v==)c++;
    }
    re(m);
    if(m<c){cout<<-;return ;}
    for(rg int i=;i<=m;++i)
        re(idx[i]);

    ST(,);
    for(rg int k=;k<=;++k)
    {
        for(rg int i=;i<=n;++i)
        {
            up[i][k]=up[up[i][k-]][k-];
            dis[i][k]=dis[up[i][k-]][k-]+dis[i][k-];
        }
    }
    while(le<ri)
    {
        rg int mid=((le+ri)>>);
        if(check(mid))ri=mid;
        else le=mid+;
    }
    cout<<le;

    return ;
}

il void re(rg int &x)
{
    rg int res=;rg int w=;char c=getchar();
    while((c<''||c>'')&&c!='-')c=getchar();
    if(c=='-')w=-,c=getchar();
    while(c>=''&&c<='')res=(res<<)+(res<<)+c-'',c=getchar();
    x=w*res;
}
void add(rg int fm,rg int to,rg int w)
{
    edge[++cnt].nt=hd[fm];
    edge[cnt].to=to;
    edge[cnt].w=w;
    hd[fm]=cnt;
}
void ST(rg int i,rg int fa)
{
    up[i][]=fa;
    for(rg int k=hd[i];k;k=edge[k].nt)
    {
        rg int qw=edge[k].to;
        if(qw==fa)continue;
        dis[qw][]=edge[k].w;
        ST(qw,i);
    }
}
int check(rg int lim){
    memset(ok,,sizeof(ok));
    memset(use,,sizeof(use));
    memset(vis,,sizeof(vis));
    rg int cnt1=,cnt2=;
    rg int top=;
    for(rg int i=;i<=m;++i){
        rg int res=lim,u=idx[i];
        for(rg int k=;k>=;--k){
            if(up[u][k]&&up[u][k]!=&&res>=dis[u][k])
                res-=dis[u][k],u=up[u][k];
        }
        if(up[u][]==&&res>dis[u][])
        {
            to[++cnt1].res=res-dis[u][];
            to[cnt1].idx=u;
        }
        else ok[u]=;
    }
    Dfs(,);
    for(rg int k=hd[];k;k=edge[k].nt){
        rg int qw=edge[k].to;
        if(!ok[qw]){
            ne[++cnt2].res=dis[qw][];
            ne[cnt2].idx=qw;
        }
    }
    sort(to+,to+cnt1+,Cmp);
    sort(ne+,ne+cnt2+,Cmp);
    if(cnt1<cnt2)return ;
    for(rg int i=;i<=cnt1;++i)
    {
        if(!vis[to[i].idx])
        {
            vis[to[i].idx]=;
            continue;
        }
        while(vis[ne[top].idx])top++;
        if(to[i].res>=ne[top].res)
        {
            vis[ne[top].idx]=,top++;
            continue;
        }
        if(top>cnt2)break;
    }
    while(vis[ne[top].idx])top++;
    if(top<=cnt2)return ;
    return ;
}
int Dfs(rg int u,rg int fa)
{
    rg int temp=,flag=;
    for(rg int k=hd[u];k;k=edge[k].nt)
    {
        rg int qw=edge[k].to;
        if(qw==fa)continue;
        flag++,temp&=Dfs(qw,u);
    }
    if(!flag)temp=;
    ok[u]=(ok[u]|temp);
    if(ok[u]&&up[u][]==)
        vis[u]=;
    return ok[u];
}
int Cmp(const S &x,const S &y){return x.res<y.res;}