如题，debug半天查不出来，求调。

#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+10;int fa[maxn];
int siz[maxn],f[maxn],son[maxn],pos1,pos2,n;
bool flag;
vector<int> vec[maxn];
void dfs(int x,int t){
	fa[x]=t;
	int tmp=0;
	siz[x]=1;
	son[t]=x;
	for(auto to:vec[x]){
		if(to==t)continue;
		dfs(to,x);
		siz[x]+=siz[to];
		tmp=max(tmp,siz[to]);
	}
	tmp=max(tmp,n-siz[x]);
	f[x]=tmp;
	if(f[x]<f[pos1]) pos1=x,pos2=0;
	if(f[x]==f[pos1]) pos2=x;
}
int S;
void dfs2(int x,int f){
	if(vec[x].size()==1){
		S=x;
		return ;
	}
	for(int y:vec[x]){
		if(y==f)continue;
		dfs2(y,x);
	}
}

int main(){
	
	int T;
	cin >> T;
	while(T--){
		f[0]=INT_MAX;
		for(int i=1;i<=n;i++){
			siz[i]=0;
			f[i]=0;
			fa[i]=0;
			vec[i].clear();
		}
		cin >> n;int x,y;
		for(int i=1;i<n;i++){
			
			cin >> x >> y;
			vec[x].push_back(y);
			vec[y].push_back(x);
		}
		dfs(1,0);
		//cout << pos1<<' '<<pos2 << endl;
		if(pos2==0||pos2==pos1){
			cout << x << ' ' << y << endl;
			cout << x << ' ' << y << endl;
			continue;
		}
		else{
			if(fa[pos1]!=pos2)swap(pos1,pos2);
			dfs2(pos1,pos2);
			printf("%d %d\n%d %d\n",S,fa[S],S,pos2);
		}
	}
}