hdu 2586 How far away ？(离线求最近公共祖先）

Posted 2020-08-13 pb2016

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<algorithm>
  4 #include<iostream>
  5 #include<vector>
  6 #include<cmath>
  7 #include<map>
  8 using namespace std;
  9 
 10 const int mx=4e4+4;
 11 struct N
 12 {
 13     int v,d;
 14     N(int x,int y)
 15     {
 16         v=x;
 17         d=y;
 18     }
 19 };
 20 vector<N>g[mx],q[mx];
 21 int father[mx];
 22 int dis[mx];
 23 bool vs[mx];
 24 int ans[mx];
 25 
 26 void Init(int n)
 27 {
 28     for (int i=1;i<=n;i++)
 29     {
 30         father[i]=i;
 31         dis[i]=0;
 32         vs[i]=false;
 33         g[i].clear();
 34         q[i].clear();
 35     }
 36 }
 37 
 38 int Find(int x)
 39 {
 40     int w=x;
 41     while (w!=father[w]) w=father[w];
 42     while (x!=father[x])
 43     {
 44         int fa=father[x];
 45         father[x]=w;
 46         x=fa;
 47     }
 48     return w;
 49 }
 50 
 51 void un(int x,int y)
 52 {
 53     int rx=Find(x);
 54     int ry=Find(y);
 55     father[y]=x;
 56 }
 57 
 58 void dfs(int u,int fa,int d)
 59 {
 60     dis[u]=d;
 61     vs[u]=true;
 62     for (int i=0;i<g[u].size();i++)
 63     {
 64         N k=g[u][i];
 65         if (vs[k.v]) continue;
 66         dfs(k.v,u,d+k.d);
 67     }
 68     for (int i=0;i<q[u].size();i++)
 69     {
 70         N k=q[u][i];
 71         if (!vs[k.v]) continue;
 72         ans[k.d]=dis[u]+dis[k.v]-2*dis[Find(k.v)];
 73     }
 74     un(fa,u);
 75 }
 76 
 77 int main()
 78 {
 79     int n,m;
 80     int t;
 81     scanf("%d",&t);
 82     while (t--)
 83     {
 84         scanf("%d%d",&n,&m);
 85         Init(n);
 86         for (int i=1;i<n;i++)
 87         {
 88             int u,v,w;
 89             scanf("%d%d%d",&u,&v,&w);
 90             g[u].push_back(N(v,w));
 91             g[v].push_back(N(u,w));
 92         }
 93         for (int i=1;i<=m;i++)
 94         {
 95             int u,v;
 96             scanf("%d%d",&u,&v);
 97             q[u].push_back(N(v,i));
 98             q[v].push_back(N(u,i));
 99         }
100         dfs(1,0,0);
101         for (int i=1;i<=m;i++) printf("%d\n",ans[i]);
102     }
103 }