先判断有几个连通块吗，因为已经满足边的个数等于顶点个数减1所以一定是一棵树，只要是1.
本来用的是优先队列，最后发现没过,其实是Error: K components 少了个s看题目一定要仔细

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 10100;
vector<int> G[MAXN];
int maxdepth = -1;
priority_queue<int,vector<int>,greater<int>> depthRoot;
bool vis[MAXN];
vector<int> temp;
set <int> s;
int happen[MAXN];
int n;
int root;
void DFS(int u,int depth)
{
    vis[u] = true;
    if(depth > maxdepth)
    {
        maxdepth = depth;
        temp.clear();
        temp.push_back(u);
    }
    else if(depth == maxdepth)
    {
        temp.push_back(u);
    }
    for(int i = 0;i<G[u].size();i++)
    {
        if(vis[G[u][i]] == false)
        {
            DFS(G[u][i],depth + 1);
        }
    }

}
int main(void)
{
    freopen("pat0314/in.txt","r",stdin);
    cin>>n;
    for(int i = 0;i<n - 1;i++)
    {
        int l,r;
        cin>>l>>r;
        G[l].push_back(r);
        G[r].push_back(l);
    }
    int num = 0;
    int s1 = 0;
    fill(vis,vis + MAXN,false);
    for(int i = 1;i<=n;i++)
    {
        if(vis[i] == false)
        {
            num++;
            DFS(i,0);
            if(i == 1)
            {
                if(temp.size() != 0)
                {
                    s1 = temp[0];
                }
                for(int k = 0;k<temp.size();k++)
                {
                    s.insert(temp[k]);
                }
                
            }
        }

    }
    if(num == 1)
    {        
        temp.clear();
        fill(vis,vis + MAXN,false);
        maxdepth = -1;
        DFS(s1,0);
        for(int i = 0;i<temp.size();i++)
        {
            s.insert(temp[i]);
        }
        for(auto it = s.begin(); it != s.end(); it++)
            printf("%d\n", *it);

    }
    else
    {
        printf("Error: %d components",num);
        return 0;
    }



    return 0;   
}