1021 Deepest Root (25 分)（太难了******）

#include <cstdio>
#include <queue>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <set>
using namespace std;
const int maxv = 20011,inf = 1<<30;


bool vis[maxv]={false};
vector<int>G[maxv];
int n,father[maxv],maxD=-1;
set<int>ans;

void init()
{
    for(int i = 1;i<=n;i++)
        father[i] = i;
}
int findFather(int x)
{
    int a = x;
    while(x!=father[x])
        x=father[x];

    while(a!=father[a])
    {
        int z = a;
        father[a] = x;
        a = father[z];
    }
    return x;
}

void Union(int a,int b)
{
    int faA = findFather(a);
    int faB = findFather(b);
    if(faA != faB)
        father[faA] = faB;
}

void Dfs(int x,int d,int pre)
{
//    vis[x] = true;
    if(d>maxD)
    {
        maxD=d;
        ans.clear();
        ans.insert(x);
    }
    else if(d == maxD)
        ans.insert(x);

    for(int i = 0;i<G[x].size();i++)
    {

        int t = G[x][i];
        if(t == pre) continue;
        Dfs(t,d+1,x);
    }
}

int main()
{
    // freopen("1.txt","r",stdin);
    scanf("%d",&n);
    for(int i = 1;i<n;i++)
    {
        int id1,id2;
        scanf("%d%d",&id1,&id2);

        G[id1].push_back(id2);
        G[id2].push_back(id1);
    }
    init();
    for(int i = 1;i<=n;i++)
    {
        for(int j = 0;j<G[i].size();j++)
        {
            int u = i,v = G[i][j];
            if(findFather(u) != findFather(v))
                Union(u,v);
        }
    }

    set<int>com;
    for(int i = 1;i<=n;i++)
    {
        int temp = findFather(i);
        com.insert(temp);
    }
    if(com.size() > 1)
        printf("Error: %d components\n",com.size());
    else
    {
        Dfs(1,1,-1);
//        for(set<int>::iterator it= ans.begin();it!=ans.end();it++)
//        {
//            printf("%d",*it);
//        }
        set<int>temp = ans;
        Dfs(*ans.begin(),1,-1);
        for(set<int>::iterator it= temp.begin();it!=temp.end();it++)
        {
            ans.insert(*it);
        }
        for(set<int>::iterator it= ans.begin();it!=ans.end();it++)
        {
            printf("%d\n",*it);
        }
    }


    return 0;
}