Vijos[1983]NOIP2015Day2T3 运输计划 transport LCA

  1 #pragma comment(linker, "/STACK:10240000,10240000")
  2 #include <cstring>
  3 #include <algorithm>
  4 #include <cstdio>
  5 #include <cstdlib>
  6 #include <cmath>
  7 #include <vector>
  8 using namespace std;
  9 const int N=300000+5,M=N*2,Inf=N*1000;
 10 void read(int &x){
 11     x=0;
 12     char ch=getchar();
 13     while (!(‘0‘<=ch&&ch<=‘9‘))
 14         ch=getchar();
 15     while (‘0‘<=ch&&ch<=‘9‘){
 16         x=x*10+ch-48;
 17         ch=getchar();
 18     }
 19 }
 20 struct Edge{
 21     int cnt,y[M],z[M],nxt[M],fst[N];
 22     void set(){
 23         cnt=0;
 24         memset(y,0,sizeof y);
 25         memset(z,0,sizeof z);
 26         memset(nxt,0,sizeof nxt);
 27         memset(fst,0,sizeof fst);
 28     }
 29     void add(int a,int b,int c){
 30         cnt++;
 31         y[cnt]=b,z[cnt]=c;
 32         nxt[cnt]=fst[a],fst[a]=cnt;
 33     }
 34 }e;
 35 int n,m;
 36 vector <int> Tree[N];
 37 int father[N],son[N],deep[N],dis[N],fadis[N],bh[N],bhtot;
 38 int Anst[N][20];//Ancestor
 39 struct Query{
 40     int x,y,LCA,cost;
 41 }q[N];
 42 int Nextsum[N];
 43 void Build_Tree(int prev,int rt){
 44     bh[++bhtot]=rt;
 45     Tree[rt].clear();
 46     deep[rt]=deep[prev]+1;
 47     son[rt]=0;
 48     father[rt]=prev;
 49     for (int i=e.fst[rt];i;i=e.nxt[i])
 50         if (e.y[i]!=prev){
 51             son[rt]++,Tree[rt].push_back(e.y[i]);
 52             fadis[e.y[i]]=e.z[i];
 53             dis[e.y[i]]=dis[rt]+e.z[i];
 54             Build_Tree(rt,e.y[i]);
 55         }
 56 }
 57 void LCA_Prepare(){
 58     memset(Anst,0,sizeof Anst);
 59     for (int i=1;i<=n;i++){
 60         int rt=bh[i];
 61         Anst[rt][0]=father[rt];
 62         for (int i=1;(1<<i)<=deep[rt];i++)
 63             Anst[rt][i]=Anst[Anst[rt][i-1]][i-1];
 64     }
 65 }
 66 int LCA(int a,int b){
 67     if (deep[a]>deep[b])
 68         swap(a,b);
 69     for (int i=deep[b]-deep[a],j=0;i>0;i>>=1,j++)
 70         if (i&1)
 71             b=Anst[b][j];
 72     if (a==b)
 73         return a;
 74     int k;
 75     for (k=0;(1<<k)<=deep[a];k++);
 76     for (;k>=0;k--)
 77         if ((1<<k)<=deep[a]&&Anst[a][k]!=Anst[b][k])
 78             a=Anst[a][k],b=Anst[b][k];
 79     return Anst[a][0];
 80 }
 81 bool check(int t){
 82     int total=0,Maxcost=0,Maxcut=0;
 83     memset(Nextsum,0,sizeof Nextsum);
 84     for (int i=1;i<=m;i++)
 85         if (q[i].cost>t){
 86             Maxcost=max(Maxcost,q[i].cost-t);
 87             total++;
 88             Nextsum[q[i].x]++;
 89             Nextsum[q[i].y]++;
 90             Nextsum[q[i].LCA]-=2;
 91         }
 92     for (int i=n;i>=1;i--)
 93         Nextsum[father[bh[i]]]+=Nextsum[bh[i]];
 94     for (int i=1;i<=n;i++)
 95         if (Nextsum[i]==total)
 96             Maxcut=max(Maxcut,fadis[i]);
 97     return Maxcost<=Maxcut;
 98 }
 99 int main(){
100     scanf("%d%d",&n,&m);
101     e.set();
102     for (int i=1;i<n;i++){
103         int a,b,c;
104         read(a),read(b),read(c);
105         e.add(a,b,c);
106         e.add(b,a,c);
107     }
108     bhtot=0;
109     deep[0]=-1,dis[1]=fadis[1]=0;
110     Build_Tree(0,1);
111     LCA_Prepare();
112     for (int i=1;i<=m;i++){
113         read(q[i].x),read(q[i].y);
114         q[i].LCA=LCA(q[i].x,q[i].y);
115         q[i].cost=dis[q[i].x]+dis[q[i].y]-dis[q[i].LCA]*2;
116     }
117     int le=0,ri=Inf,mid,ans=0;
118     while (le<=ri){
119         mid=(le+ri)>>1;
120         if (check(mid))
121             ri=mid-1,ans=mid;
122         else
123             le=mid+1;
124     }
125     printf("%d",ans);
126     return 0;
127 }