POJ 3107 求树的重心

#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;
}