1021.Deepest Root (并查集+DFS树的深度)

A graph which is connected and acyclic can be considered a tree. The height of the tree depends on the selected root. Now you are supposed to find the root that results in a highest tree. Such a root is called the deepest root.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=10000) which is the number of nodes, and hence the nodes are numbered from 1 to N. Then N-1 lines follow, each describes an edge by given the two adjacent nodes' numbers.

Output Specification:

For each test case, print each of the deepest roots in a line. If such a root is not unique, print them in increasing order of their numbers. In case that the given graph is not a tree, print "Error: K components" where K is the number of connected components in the graph.

Sample Input 1:

5

1 2

1 3

1 4

2 5

Sample Output 1:

3

4

5

Sample Input 2:

5

1 3

1 4

2 5

3 4

Sample Output 2:

Error: 2 components

 #include <iostream>

 #include <vector>

 #include <queue>

 using namespace std;

 vector<int> adj[];
 int visit[];
 int Tree[];
 int root[];
 int MM[];
 int num;
 int getroot(int x)

 {

     if(Tree[x]==-)  return x;

     else

     {
         int tem=getroot(Tree[x]);
         Tree[x]=tem;
         return tem;
     }

 }

 void DFS(int x,int d)

 {
     visit[x]=;
     int i;
     for(i=;i<adj[x].size();i++)
     {

         if(visit[adj[x][i]]==)
             DFS(adj[x][i],d+);
     }
     root[num++]=d;
 }

 int main()

 {
     int n,a,b,i,j;
     while(cin>>n)
     {
         for(i=;i<=n;i++)//初始化
         {
             Tree[i]=-;
             adj[i].clear();
         }
         for(i=;i<n-;i++)
         {
             cin>>a>>b;
             adj[a].push_back(b);
             adj[b].push_back(a);
             a=getroot(a);//并查集
             b=getroot(b);
             if(a!=b)
             {
                 Tree[a]=b;
             }
         }
         int count=;//极大连通图个数
         for(i=;i<=n;i++)
         {
             if(Tree[i]==-) count++;
         }
         if(count!=)
         {
             cout<<"Error: "<<count<<" components"<<endl;//不是树
         }
         else
         {
             for(i=;i<=n;i++)
             {
                 for(j=;j<=n;j++)//每次查找都要初始化
                     visit[j]=;
                 num=;
                 DFS(i,);
                 MM[i]=;
                 for(j=;j<num;j++)
                 {
                     if(MM[i]<root[j])
                         MM[i]=root[j];
                 }
             }
             int max=;
             for(i=;i<=n;i++)
             {
                 if(max<MM[i])
                     max=MM[i];
             }
             for(i=;i<=n;i++)
             {
                 if(max==MM[i])
                     cout<<i<<endl;
             }
         }
     }
     return ;
 }