BZOJ 2286 树链剖分+DFS序+虚树+树形DP

第一次学习虚树，就是把无关的点去掉。Ｓ里维护一条链即可。

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 #include <algorithm>
 #define LL long long
 using namespace std;
 const LL Maxm=;
 const LL Maxn=;
 const LL Inf=1e60;
 struct Node {LL to,next,w;}edge[Maxm],edge2[Maxm];
 LL head[Maxn],head2[Maxn],dep[Maxn],H[Maxn],mark[Maxn],size[Maxn];
 LL top[Maxn],father[Maxn],f[Maxn],S[Maxn],mn[Maxn];
 LL cnt1,cnt2,tot,n,u,v,w,tp,m,K;
 bool vis[Maxn];
 inline void Add(LL u,LL v,LL w)
 {edge[cnt1].to=v;edge[cnt1].next=head[u];edge[cnt1].w=w;head[u]=cnt1++;
 edge[cnt1].to=u;edge[cnt1].next=head[v];edge[cnt1].w=w;head[v]=cnt1++;}
 inline void Add2(LL u,LL v)
 {if (u==v) return; edge2[cnt2].to=v;edge2[cnt2].next=head2[u];head2[u]=cnt2++;}
 inline LL Min(LL x,LL y) {return x>y?y:x;}
 inline void Get_Int(LL &x)
 {
     x=;  char ch=getchar(); LL f=;
     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}
     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();} x*=f;
 }
 inline void Put_Int(LL x)
 {
     char ch[];  LL top=;
     if (x==) ch[++top]='';
     while (x) ch[++top]=x%+'',x/=;
     while (top) putchar(ch[top--]); putchar('\n');
 }
 //================================================
 void Dfs1(LL u)
 {
     mark[u]=++tot;vis[u]=true; size[u]=;
     for (LL i=head[u];i!=-;i=edge[i].next)
         if (!vis[edge[i].to])
         {
             dep[edge[i].to]=dep[u]+;
             father[edge[i].to]=u;
             mn[edge[i].to]=Min(mn[u],edge[i].w);
             Dfs1(edge[i].to);
             size[u]+=size[edge[i].to];
         }
 }
 void Dfs2(LL u,LL chain)
 {
     top[u]=chain; vis[u]=true; LL k=;
     for (int i=head[u];i!=-;i=edge[i].next)
         if (!vis[edge[i].to] && (size[edge[i].to]>size[k] || k==)) k=edge[i].to;
     if (k==) return;
     Dfs2(k,chain);
     for (int i=head[u];i!=-;i=edge[i].next)
         if (!vis[edge[i].to] && i!=k) Dfs2(edge[i].to,edge[i].to);
 }
 inline LL Lca(LL u,LL v)
 {
     while (true)
     {
         if (top[u]==top[v]) return dep[u]>dep[v]?v:u;
         if (dep[top[u]]>dep[top[v]]) u=father[top[u]];
         else v=father[top[v]];
     }
 }
 //=============================================================
 inline bool cmp(LL x,LL y) {return mark[x]<mark[y];}
 void Dp(LL u)
 {

     vis[u]=true; f[u]=mn[u]; LL ret=;
     for (int i=head2[u];i!=-;i=edge2[i].next)
     {
         Dp(edge2[i].to);
         ret+=f[edge2[i].to];
     }
     head2[u]=-;
     if (ret) f[u]=Min(f[u],ret);
 }
 void Solve()
 {
     Get_Int(K);
     for (int i=;i<=K;i++) Get_Int(H[i]);
     sort(H+,H+K+,cmp);
     tp=tot=; H[++tot]=H[];
     for (int i=;i<=K;i++)
         if (Lca(H[tot],H[i])!=H[tot]) H[++tot]=H[i];
     cnt2=;
     S[++tp]=;
     for (int i=;i<=tot;i++)
     {
         LL u=H[i],f=Lca(u,S[tp]);
         while (true)
         {
             if (dep[f]>=dep[S[tp-]])
             {
                 Add2(f,S[tp--]);
                 if (S[tp]!=f) S[++tp]=f;
                 break;
             }
             Add2(S[tp-],S[tp]); tp--;
         }
         if (S[tp]!=u) S[++tp]=u;
     }
     while (--tp) Add2(S[tp],S[tp+]);
     Dp();
     Put_Int(f[]);
 }
 int main()
 {
     Get_Int(n);
     memset(head,-,sizeof(head));cnt1=;
     for (int i=;i<n;i++)
     {
         Get_Int(u),Get_Int(v),Get_Int(w);
         Add(u,v,w),Add(v,u,w);
     }

     father[]=; dep[]=; tot=; mn[]=Inf;
     memset(vis,false,sizeof(vis));Dfs1();
     memset(vis,false,sizeof(vis));Dfs2(,);
     memset(head2,-,sizeof(head2));
     Get_Int(m);
     for (int i=;i<=m;i++) Solve();
     return ;
 }

C++