URAL1056[Computer net]

想到了NOIP2007的core，然后先求出树的直径（从一点DFS找最远点，再从最远点DFS找最远点，两个最远点的距离为直径）。然后由一条直径的两个端点分别标记距它们不超过(直径+1)/2的点，两次都被标记的就输出。

CODE:

/*

PROGRAM: $PROGRAM

AUTHOR: Su Jiao

DATE: 2010-3-28

DESCRIPTION:

$DESCRIPTION

*/

#include <iostream>

using std::cin;

using std::cout;

#include <fstream>

using std::ifstream;

using std::ofstream;

#include <sstream>

using std::stringstream;

using std::endl;

#include <vector>

using std::vector;

#include <string>

using std::string;

#include <stack>

using std::stack;

#include <queue>

using std::queue;

#include <set>

using std::set;

#include <map>

using std::map;

using std::pair;

using std::make_pair;

#include <algorithm>

using std::sort;

#include <cassert>

//using std::assert;

 

class Application

{

      int N;

      vector<vector<int> > link;

      int max;

      int maxid;

      vector<bool> visited;

      vector<int> mark;

      void dfs(int node,int depth=0)

      {

           if (visited[node]) return;

          

           visited[node]=true;

           if (depth>max)

           {

              max=depth;

              maxid=node;

           }

           for (int i=0;i<link[node].size();i++)

               dfs(link[node][i],depth+1);

           visited[node]=false;

      }

      void dfs_mark(int node,int R)

      {

           if (visited[node]) return;

           if (R<0) return;

          

           visited[node]=true;

           mark[node]++;

           for (int i=0;i<link[node].size();i++)

               dfs_mark(link[node][i],R-1);

           visited[node]=false;

      }

      public:

      Application()

      {

                   cin>>N;

                   link.resize(N);

                   for (int i=1,p;i<N;i++)

                       cin>>p,link[p-1].push_back(i),link[i].push_back(p-1);

      }

      int run()

      {

          int head,tail,R;

          visited.resize(N,false);

         

          max=0;

          dfs(0);

          head=maxid;

         

          max=0;

          dfs(maxid);

          tail=maxid;

         

          R=(max+1)/2;

         

          mark.resize(N,0);

          dfs_mark(head,R);

          dfs_mark(tail,R);

         

          vector<int> answer;

          for (int i=0;i<N;i++)

              if (mark[i]==2) answer.push_back(i+1);

          for (int i=0;i<answer.size();i++)

              cout<<answer[i]<<char(i+1==answer.size()?’\n’:’ ‘);

          return 0;

      }

};

 

int main()

{

    Application app;

    return app.run();

}