2286: [Sdoi2011]消耗战

2286: [Sdoi2011]消耗战

链接

分析

　　虚树练习题。

　　构建虚树，在虚树上DP。

　　

　　跟着gxb学虚-tree。。。

代码

 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <iostream>
 #include <cmath>
 #include <cctype>

 using namespace std;

 const int N = ;
 const int INF = 1e9;

 int head[N<<],nxt[N<<],to[N<<],w[N<<],TotE;
 int deth[N],val[N],siz[N],dfn[N],fa[N],son[N],bel[N],sk[N<<],top,Time_index;
 int A[N];

 inline int read() {
     int x = ,f = ;char ch =getchar();
     for (; !isdigit(ch); ch=getchar()) if (ch=='-') f=-;
     for (; isdigit(ch); ch=getchar()) x = x*+ch-'';
     return x * f;
 }
 bool cmp(const int &a,const int &b) {
     return dfn[a] < dfn[b];
 }
 void Add_edge(int u,int v,int c) {
     ++TotE;to[TotE] = v;w[TotE] = c;nxt[TotE] = head[u];head[u] = TotE;
     ++TotE;to[TotE] = u;w[TotE] = c;nxt[TotE] = head[v];head[v] = TotE;
 }
 void add_edge(int u,int v) {
     ++TotE;to[TotE] = v;nxt[TotE] = head[u];head[u] = TotE;
 }
 void dfs1(int u,int mn) {
     val[u] = mn;
     siz[u] = ;
     for (int i=head[u]; i; i=nxt[i]) {
         int v = to[i];
         if (v==fa[u]) continue;
         fa[v] = u;
         deth[v] = deth[u] + ;
         dfs1(v,min(w[i],mn));
         siz[u] += siz[v];
         if (!son[u] || siz[v] > siz[son[u]]) son[u] = v;
     }
 }
 void dfs2(int u,int top) {
     bel[u] = top;
     dfn[u] = ++Time_index;
     if (!son[u]) return;
     dfs2(son[u],top);
     for (int i=head[u]; i; i=nxt[i]) {
         int v = to[i];
         if (v==fa[u] || v==son[u]) continue;
         dfs2(v,v);
     }
 }
 int Lca(int u,int v) {
     while (bel[u] != bel[v]) {
         if (deth[bel[u]] < deth[bel[v]]) swap(u,v);
         u = fa[bel[u]];
     }
     if (deth[u] < deth[v]) return u;
     return v;
 }
 void Insert(int p) {
     int x = sk[top];
     if (x==) {sk[++top] = p;return ;}
     int lca = Lca(p,x);
     if (lca == x) return; // 此题构建虚树不同的是，若x==lca，不加入p。
     while (lca != x) {
         int y = sk[--top];
         if (dfn[y] < dfn[lca]) {
             add_edge(lca,x);
             sk[++top] = lca;
             break;
         }
         add_edge(y,x);
         x = sk[top];
     }
     sk[++top] = p;
 }
 long long DP(int u) {
     if (!head[u]) return val[u];
     long long ans = ;
     for (int i=head[u]; i; i=nxt[i]) ans += DP(to[i]);
     head[u] = ;
     return min(ans,(long long)val[u]);
 }
 int main() {
     int n = read();
     for (int i=; i<n; ++i) {
         int u = read(),v = read(),w = read();
         Add_edge(u,v,w);
     }
     deth[] = ;
     dfs1(,INF);
     dfs2(,);
     TotE = ;
     memset(head,,sizeof(head));

     int m = read();
     while (m--) {
         TotE = ;sk[top = ] = ;

         int k = read();
         for (int i=; i<=k; ++i) A[i] = read();
         sort(A+,A+k+,cmp);
         for (int i=; i<=k; ++i) Insert(A[i]);
         while (--top) add_edge(sk[top],sk[top+]);

         long long ans = ;
         for (int i=head[]; i; i=nxt[i]) ans += DP(to[i]); // 单独处理1的情况，否则val[1]设为很大的longlong数，INF不够。
         printf("%lld\n",ans);
         head[] = ;
     }
     return ;
 }