https://codeforc.es/contest/1176/problem/E
题意:选不超n/2个点使得每个没选的最少连一个选了的点;
思路:隔层取,答案是最少点数的;
#include<algorithm>
#include<set>
#include<queue>
#include<cmath>
#include<cstring>
#include<iostream>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstdio>
#include<map>
#include<stack>
#include<string>
#include<bits/stdc++.h>
using namespace std;
#define sfi(i) scanf("%d",&i)
#define sfs(i) scanf("%s",(i))
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define ull unsigned long long
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-16
#define PI acos(-1)
#define lowbit(x) ((x)&(-x))
#define zero(x) (((x)>0?(x):-(x))<eps)
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define endl '\n'
#define pb push_back
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid+1,r
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
const int maxn=1e6+9;
const int mod=1e9+7;
inline ll read()
{
ll f=1,x=0;
char ss=getchar();
while(ss<'0'||ss>'9')
{
if(ss=='-')f=-1;ss=getchar();
}
while(ss>='0'&&ss<='9')
{
x=x*10+ss-'0';ss=getchar();
} return f*x;
}
vector<int>g[maxn];
vector<int>sum[3];
int n,m;
bool vis[maxn];
void dfs(int u,int id,int fa)
{
if(vis[u]) return ;
sum[id].pb(u);
vis[u]=1;
for(int i=0;i<g[u].size();i++)
{
int v=g[u][i];
if(v==fa) continue;
dfs(v,id^1,u);
}
}
int main()
{
//FAST_IO;
//freopen("input.txt","r",stdin);
int t;
cin>>t;
while(t--)
{
cin>>n>>m;
for(int i=0;i<=n;i++) vis[i]=0,g[i].clear();
sum[1].clear();
sum[0].clear();
while(m--)
{
int u,v;
cin>>u>>v;
g[u].pb(v);
g[v].pb(u);
}
dfs(1,1,-1);
if(sum[1].size()>sum[0].size())
{
cout<<sum[0].size()<<endl;
for(int i=0;i<sum[0].size();i++)
{
cout<<sum[0][i]<<" ";
}
cout<<endl;
}
else
{
cout<<sum[1].size()<<endl;
for(int i=0;i<sum[1].size();i++)
{
cout<<sum[1][i]<<" ";
}
cout<<endl;
}
}
}