noip2015运输计划

二分+LCA+查分前缀和

 #include<iostream>
 #include<cstring>
 #include<cstdio>
 #include<algorithm>
 using namespace std;
 int read()
 {
     int x=,f=;char ch;ch=getchar();
     while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}
     while(ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}
     return x*f;
 }
 struct data{int to,next,v,from;}e[];
 struct data2{int to,next,from,num;}as[];
 int lca[],dis[];
 int head[],head2[],cnt;
 void add(int u,int v,int w){e[cnt].from=u,e[cnt].to=v,e[cnt].next=head[u],e[cnt].v=w,head[u]=cnt;cnt++;}
 void add2(int u,int v,int nu){as[cnt].to=v,as[cnt].next=head2[u],as[cnt].from=u,as[cnt].num=nu,head2[u]=cnt,cnt++;}
 int n,m,l=,r=;
 int d[];
 bool vis[];
 int fa[];
 int p[];
 int s[],t1[];
 int find(int x){return x==fa[x]?fa[x]:fa[x]=find(fa[x]);}
 int maxn=,maxj=;
 void dfs(int now,int d)
 {
     dis[now]=d;
     vis[now]=;
     for(int i=head[now];i>=;i=e[i].next) if(!vis[e[i].to]) dfs(e[i].to,d+e[i].v);
 }
 void Lca(int now)
 {
     vis[now]=;
     for(int i=head[now];i>=;i=e[i].next)
         if(!vis[e[i].to])
         {
             Lca(e[i].to);fa[find(e[i].to)]=find(now);
         }
     for(int i=head2[now];i>=;i=as[i].next)
     {
         if(vis[as[i].to])
         {
             lca[as[i].num]=find(as[i].to);
             //cout<<dis[as[i].from]<<' '<<dis[as[i].to]<<' '<<2*dis[lca[as[i].num]]<<endl;
             d[as[i].num]=abs(dis[as[i].from]+dis[as[i].to]-*dis[lca[as[i].num]]);
             r=max(r,d[as[i].num]);
         }
     }
 }
 int work(int now,int t,int from)
 {
     int sum=p[now];
     for(int i=head[now];i>=;i=e[i].next)
         if(e[i].to!=from) sum+=work(e[i].to,t,e[i].from);
     if(sum==t)maxj=max(maxj,dis[now]-dis[from]);
     return sum;
 }
 bool check(int mid,int t)
 {
     work(,t,);
     if(maxn-maxj<=mid) return ;
     else return ;
 }
 int main()
 {
     memset(head,-,sizeof(head));
     memset(head2,-,sizeof(head2));
     n=read(),m=read();
     for(int i=;i<=n;i++) fa[i]=i;
     for(int i=;i<n;i++)
     {
         int u,v,w;
         u=read(),v=read(),w=read();
         add(u,v,w);
         add(v,u,w);
     }
     cnt=;
     for(int i=;i<=m;i++)
     {
         s[i]=read(),t1[i]=read();
         add2(s[i],t1[i],i);
         add2(t1[i],s[i],i);
     }
     dfs(,);
     memset(vis,,sizeof(vis));
     Lca();
     //for(int i=1;i<=n;i++) cout<<dis[i]<<endl;
     //for(int i=1;i<=m;i++) cout<<d[i]<<endl;
     while(l<=r)
     {
         int t=;
         int mid=(l+r)>>;
         maxj=;
         memset(p,,sizeof(p));
         for(int i=;i<=m;i++)
         {
             if(d[i]>mid){maxn=max(maxn,d[i]);t++;p[s[i]]++,p[t1[i]]++,p[lca[i]]-=;}
         }
         if(check(mid,t)) r=mid-;
         else l=mid+;
     }
     cout<<l;
     return ;
 }