1021. deepest root

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 calledThe 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.

I was trying to solve the brute-force problem. I didn't find a clue for a long time, and then I saw the logic of the great god.

Traverse from any node. The deepest node obtained must be part of the root node set. The result of the traversal is the root node set.

#include <stdio.h>#include <stdlib.h>#include <vector>#include <set>using namespace std;#define N 10001vector<int> G[N];int father[N];set<int> root;int maxH=0;set<int> temp,result;void DFS (int now,int height,int pre);int Block(int n);int Find (int a);void Union (int a,int b);void Init (int n);int main (){    int n,i;    scanf("%d",&n);    Init(n);    int start,end;    for( i=0;i<n-1;i++)    {         scanf("%d %d",&start,&end);         G[start].push_back(end);         G[end].push_back(start);         Union(start,end);         }    //////////////////    int num=Block(n);    if( num>1)    {        printf("Error: %d components\n",num);        return 0;        }    DFS(1,1,-1);    result=temp;    set<int>::iterator it=result.begin();    set<int>::iterator its=temp.begin();    DFS(*it,1,-1);    for( ;its!=temp.end();its++) result.insert(*its);    for( it=result.begin();it!=result.end();it++) printf("%d\n",*it);    system("pause");    return 0;    }void DFS (int now,int height,int pre){     if( height>maxH)     {         temp.clear();         temp.insert(now);         maxH=height;         }     else if( height==maxH) temp.insert(now);          for(int i=0;i<G[now].size();i++)         if(G[now][i]!=pre) DFS(G[now][i],height+1,now);     }int Block(int n){    int i;    for( i=1;i<=n;i++) root.insert(Find(i));    return root.size();    }int Find (int a){    while( a!=father[a]) a=father[a];    return a;    }void Union (int a,int b){     int fa=Find(a);     int fb=Find(b);     if( fa!=fb) father[fa]=fb;     }void Init (int n){     int i;     for( i=1;i<=n;i++)          father[i]=i;     }

1021. deepest root