【HDU 2586】测板

来源：互联网发布：淘宝关闭订单规则编辑：程序博客网时间：2024/04/26 21:58
tarjan - LCA
O(n+q)
#pragma comment(linker, "/STACK:1024000000,1024000000")  #include <iostream>  #include <string.h>  #include <stdio.h>  #include <vector>  using namespace std;  const int N = 50005;  vector<int> v[N],w[N],query[N],num[N];  int pre[N],dist[N],ans[N];  bool vis[N];  int n;  void Init()  {      for(int i=1; i<=n; i++)      {          v[i].clear();          w[i].clear();          query[i].clear();          num[i].clear();          pre[i] = i;          dist[i] = 0;          vis[i] = false;      }  }  int Find(int x)  {      if(pre[x] != x)          pre[x] = Find(pre[x]);      return pre[x];  }  void Union(int x,int y)  {      x = Find(x);      y = Find(y);      if(x == y) return;      pre[y] = x;  }  void Tarjan(int cur,int val)  {      vis[cur] = true;      dist[cur] = val;      int size = v[cur].size();      for(int i=0;i<size;i++)      {          int tmp = v[cur][i];          if(vis[tmp]) continue;          Tarjan(tmp,val + w[cur][i]);          Union(cur,tmp);      }      int Size = query[cur].size();      for(int i=0;i<Size;i++)      {          int tmp = query[cur][i];          if(!vis[tmp]) continue;          ans[num[cur][i]] = dist[cur] + dist[tmp] - 2*dist[Find(tmp)];      }  }  int main()  {      int T,Q,x,y,z;      scanf("%d",&T);      while(T--)      {          scanf("%d%d",&n,&Q);          Init();          for(int i=1;i<n;i++)          {              scanf("%d%d%d",&x,&y,&z);              v[x].push_back(y);              w[x].push_back(z);              v[y].push_back(x);              w[y].push_back(z);          }          for(int i=0;i<Q;i++)          {              scanf("%d%d",&x,&y);              query[x].push_back(y);              query[y].push_back(x);              num[x].push_back(i);              num[y].push_back(i);          }          Tarjan(1,0);          for(int i=0;i<Q;i++)             printf("%d\n",ans[i]);      }      return 0;  }
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