HDU 2586 How far away?

  1 #include <iostream>
  2 #include <cstring>
  3 #include <cstdio>
  4 #include <cstdlib>
  5 #include <cmath>
  6 #include <string>
  7 #include <vector>
  8 #include <list>
  9 #include <map>
 10 #include <queue>
 11 #include <stack>
 12 #include <bitset>
 13 #include <algorithm>
 14 #include <numeric>
 15 #include <functional>
 16 #include <set>
 17 #include <fstream>
 18 
 19 using namespace std;
 20 
 21 const int maxn=40010;
 22 
 23 struct edge{
 24     int from,to,cost,next;
 25 };
 26 edge es[maxn*2];
 27 int head[maxn],idx;
 28 int dis[maxn],N,M;
 29 int U[maxn],V[maxn];
 30 int par[maxn],rankh[maxn];
 31 int LCA[maxn];
 32 bool used[maxn];
 33 
 34 void add_edge(int u,int v,int cost)
 35 {
 36     es[idx].from=u;
 37     es[idx].to=v;
 38     es[idx].cost=cost;
 39     es[idx].next=head[u];
 40     head[u]=idx++;
 41 }
 42 
 43 void build_graph(int u,int v,int cost)
 44 {
 45     add_edge(u,v,cost);
 46     add_edge(v,u,cost);
 47 }
 48 
 49 void init(int n)
 50 {
 51     for(int i=0;i<=n;i++)
 52     {
 53         par[i]=i;
 54         rankh[i]=0;
 55     }
 56 }
 57 
 58 int find(int x)
 59 {
 60     if(x==par[x]) return x;
 61     else return par[x]=find(par[x]);
 62 }
 63 
 64 void tarjan(int u)
 65 {
 66     used[u]=true;
 67     for(int  i=0;i<M;i++)
 68     {
 69         if(U[i]==u&&used[V[i]]) LCA[i]=find(V[i]);
 70         if(V[i]==u&&used[U[i]]) LCA[i]=find(U[i]);
 71     }
 72     for(int i=head[u];i!=-1;i=es[i].next)
 73     {
 74         int v=es[i].to;
 75         if(!used[v]){
 76             dis[v]=dis[u]+es[i].cost;
 77             tarjan(v);
 78             par[v]=u;
 79         }
 80     }
 81 }
 82 
 83 int main()
 84 {
 85 //    freopen("/Users/apple/Desktop/暑假/HDU 2586/HDU 2586/in","r",stdin);
 86     int T;
 87     scanf("%d",&T);
 88     while(T--)
 89     {
 90         scanf("%d%d",&N,&M);
 91         init(2*N);
 92         memset(head,-1,sizeof(head));
 93         idx=0;
 94         memset(used,false,sizeof(used));
 95         dis[1]=0;
 96         for(int i=0;i<=N;i++)
 97         {
 98             U[i]=V[i]=LCA[i]=0;
 99         }
100         for(int i=0;i<N-1;i++)
101         {
102             int u,v,cost;
103             scanf("%d%d%d",&u,&v,&cost);
104             build_graph(u, v, cost);
105         }
106         for(int i=0;i<M;i++)
107         {
108             int u,v;
109             scanf("%d%d",&u,&v);
110             U[i]=u,V[i]=v;
111         }
112         tarjan(1);
113         for(int i=0;i<M;i++)
114         {
115             int res=dis[U[i]]+dis[V[i]]-2*dis[LCA[i]];
116             printf("%d\n",res);
117         }
118     }
119     return 0;
120 }