Wannafly挑战赛1 C MMSet2 虚树
题目链接:https://www.nowcoder.com/acm/contest/15/C
思路:虚树,取两点间的lca,构造成一颗新的树;求(直径+1)/2即可
#pragma comment(linker, "/STACK:1024000000,1024000000") #include<iostream> #include<cstdio> #include<cmath> #include<string> #include<queue> #include<algorithm> #include<stack> #include<cstring> #include<vector> #include<list> #include<set> #include<map> #include<bitset> #include<time.h> using namespace std; #define LL long long #define pi (4*atan(1.0)) #define eps 1e-8 #define bug(x) cout<<"bug"<<x<<endl; const int N=3e5+10,M=1e6+10,inf=1e9+7,MOD=1e9+7; const LL INF=1e18+10,mod=1e9+7; struct edge { int v,next; }edge[N<<1]; int head[N],fa[N][20],edg,deep[N]; int in[N],out[N],tot; void init() { memset(head,-1,sizeof(head)); edg=0;tot=0; } void add(int u,int v) { edg++; edge[edg].v=v; edge[edg].next=head[u]; head[u]=edg; } void dfs(int u,int fat) { tot++; in[u]=tot; for (int i=1; i<=19 ;i++) fa[u][i] = fa[fa[u][i-1]][i-1]; for (int i=head[u];i!=-1;i=edge[i].next) { int v=edge[i].v; if(v==fat) continue; deep[v]=deep[u]+1; fa[v][0]=u; dfs(v,u); } out[u]=tot; } int RMQ_LCA(int x,int y) { if(deep[x]<deep[y]) swap(x,y); int d=deep[x]-deep[y]; for (int i=0; i<=19 ;i++) if((1<<i)&d) x=fa[x][i]; for (int i=19; i>=0 ;i--) { if(fa[x][i]!=fa[y][i]) { x=fa[x][i];y=fa[y][i]; } } if(x==y) return x; else return fa[x][0]; } int h[M],ans,far,pos; struct f { int v,w,nex; }edge2[N<<1]; int head2[N],edg2; void add2(int u,int v,int w) { edge2[++edg2]=(f){v,w,head2[u]}; head2[u]=edg2; } bool cmp(int u, int v) { return in[u] < in[v]; } bool check(int u, int v) { return in[u] <= in[v] && in[v] <= out[u]; } int build(int A[], int tot) { std::sort(A + 1, A + 1 + tot, cmp); for(int i = 2, old_tot = tot; i <= old_tot; i++) { A[++tot] = RMQ_LCA(A[i - 1], A[i]); } std::sort(A + 1, A + 1 + tot, cmp); tot = std::unique(A + 1, A + 1 + tot) - A - 1; std::stack<int> S; S.push(A[1]); for(int i = 2; i <= tot; i++) { while(!S.empty() && !check(S.top(), A[i])) S.pop(); int u = S.top(), v = A[i]; add2(u,v,deep[v]-deep[u]); add2(v,u,deep[v]-deep[u]);//u, v, deep[v] - deep[u]); S.push(v); } return tot; } void dfs1(int u,int fa,int val) { if(val>far)far=val,pos=u; for(int i=head2[u];i!=-1;i=edge2[i].nex) { int v=edge2[i].v; int w=edge2[i].w; if(v==fa)continue; dfs1(v,u,val+w); } } void dfs2(int u,int fa,int val) { ans=max(ans,val); for(int i=head2[u];i!=-1;i=edge2[i].nex) { int v=edge2[i].v; int w=edge2[i].w; if(v==fa)continue; dfs2(v,u,w+val); } } int main() { init(); memset(head2,-1,sizeof(head2)); int n; scanf("%d",&n); for(int i=1;i<n;i++) { int u,v; scanf("%d%d",&u,&v); add(u,v);add(v,u); } dfs(1,0); int q; scanf("%d",&q); while(q--) { edg2=far=pos=ans=0; int t; scanf("%d",&t); for(int i=1;i<=t;i++) scanf("%d",&h[i]); t = build(h, t); dfs1(h[1],0,0); dfs2(pos,0,0); printf("%d\n",(ans+1)/2); for(int i=1;i<=t;i++) head2[h[i]]=-1; } return 0; }
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