題意：求出樹的所有重心編號，從小到大排序輸出

#include<cstring>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<queue>
#include<vector>
#include<map>
#include<list>
#include<stack>
#include<climits>
 

#include<cctype>
#include<bitset>
#include<set>
#include<sstream>
#include<climits>
using namespace std;
#define mod 1000000007
#define PI acos(-1.0)
#define INF 0x3f3f3f3f
typedef long long LL;
typedef unsigned long long ULL;

const int maxn=50005;
struct edge{
    int to,next;
}E[maxn<<1
 
];
int n,tol,num;
int son[maxn];
int head[maxn];
bool vis[maxn];
int ans[maxn];
int siz;
void init(){
    siz=INF;
    tol=0;
    memset(vis,0,sizeof(vis));
    memset(head,-1,sizeof(head));
    memset(son,0,sizeof(son));
}
void add(int u,int v){
    E[tol].to=v;
    E[tol].next=head[u];
    head[u]=tol++;
}
void
 
 dfs(int u){
    vis[u]=1;
    son[u]=0;
    int tmp=0;
    for(int i=head[u];i!=-1;i=E[i].next){
        int to=E[i].to;
        if(!vis[to]){
            dfs(to);
            son[u]+=son[to]+1;
            tmp=max(tmp,son[to]+1);
        }
    }
    tmp=max(tmp,n-son[u]-1);
    if(tmp<siz){
         num=0;
         siz=tmp;
         ans[num++]=u;
    }
    else if(tmp==siz){
        ans[num++]=u;
    }
}


int main()
{
    while(~scanf("%d",&n)){
        init();
        for(int i=1;i<=n-1;i++){
            int u,v;
            scanf("%d%d",&u,&v);
            add(u,v);
            add(v,u);
        }
        dfs(1);
        sort(ans,ans+num);
        printf("%d",ans[0]);
        for(int i=1;i<num;i++){
            printf(" %d",ans[i]);
        }
        printf("\n");
    }
    return 0;
}