noip2015运输计划

  1 #include<iostream>
  2 #include<cstring>
  3 #include<cstdio>
  4 #include<algorithm>
  5 using namespace std;
  6 int read()
  7 {
  8     int x=0,f=1;char ch;ch=getchar();
  9     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();} 
 10     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();} 
 11     return x*f;
 12 }
 13 struct data{int to,next,v,from;}e[600001];
 14 struct data2{int to,next,from,num;}as[600001];
 15 int lca[300001],dis[300001];
 16 int head[300001],head2[300001],cnt;
 17 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++;}
 18 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++;}
 19 int n,m,l=0,r=0;
 20 int d[300001];
 21 bool vis[300001];
 22 int fa[300001];
 23 int p[300001];
 24 int s[300001],t1[300001];
 25 int find(int x){return x==fa[x]?fa[x]:fa[x]=find(fa[x]);}
 26 int maxn=0,maxj=0;
 27 void dfs(int now,int d)
 28 {
 29     dis[now]=d;
 30     vis[now]=1;
 31     for(int i=head[now];i>=0;i=e[i].next) if(!vis[e[i].to]) dfs(e[i].to,d+e[i].v);
 32 }
 33 void Lca(int now)
 34 {
 35     vis[now]=1;
 36     for(int i=head[now];i>=0;i=e[i].next)
 37         if(!vis[e[i].to])
 38         {
 39             Lca(e[i].to);fa[find(e[i].to)]=find(now);
 40         }
 41     for(int i=head2[now];i>=0;i=as[i].next)
 42     {
 43         if(vis[as[i].to])
 44         {
 45             lca[as[i].num]=find(as[i].to);
 46             //cout<<dis[as[i].from]<<‘ ‘<<dis[as[i].to]<<‘ ‘<<2*dis[lca[as[i].num]]<<endl;
 47             d[as[i].num]=abs(dis[as[i].from]+dis[as[i].to]-2*dis[lca[as[i].num]]);
 48             r=max(r,d[as[i].num]);
 49         }
 50     }
 51 }
 52 int work(int now,int t,int from)
 53 {
 54     int sum=p[now];
 55     for(int i=head[now];i>=0;i=e[i].next)
 56         if(e[i].to!=from) sum+=work(e[i].to,t,e[i].from);
 57     if(sum==t)maxj=max(maxj,dis[now]-dis[from]);
 58     return sum;
 59 }
 60 bool check(int mid,int t)
 61 {
 62     work(1,t,0);
 63     if(maxn-maxj<=mid) return 1;
 64     else return 0;
 65 }
 66 int main()
 67 {
 68     memset(head,-1,sizeof(head));
 69     memset(head2,-1,sizeof(head2));
 70     n=read(),m=read();
 71     for(int i=1;i<=n;i++) fa[i]=i;
 72     for(int i=1;i<n;i++)
 73     {
 74         int u,v,w;
 75         u=read(),v=read(),w=read();
 76         add(u,v,w);
 77         add(v,u,w);
 78     }
 79     cnt=0;
 80     for(int i=1;i<=m;i++)
 81     {
 82         s[i]=read(),t1[i]=read();
 83         add2(s[i],t1[i],i);
 84         add2(t1[i],s[i],i);
 85     }
 86     dfs(1,0);
 87     memset(vis,0,sizeof(vis));
 88     Lca(1);
 89     //for(int i=1;i<=n;i++) cout<<dis[i]<<endl;
 90     //for(int i=1;i<=m;i++) cout<<d[i]<<endl;
 91     while(l<=r)
 92     {
 93         int t=0;
 94         int mid=(l+r)>>1;
 95         maxj=0;
 96         memset(p,0,sizeof(p));
 97         for(int i=1;i<=m;i++)
 98         {
 99             if(d[i]>mid){maxn=max(maxn,d[i]);t++;p[s[i]]++,p[t1[i]]++,p[lca[i]]-=2;}
100         }
101         if(check(mid,t)) r=mid-1;
102         else l=mid+1;
103     }
104     cout<<l;
105     return 0;
106 }