Cover it!

https://codeforces.com/contest/1176/problem/E

C++版本一

题解：二分图01染色

C++版本二

题解：贪心

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=200000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,u,v;
int ans,cnt,flag,temp,sum;
int vis[N],c[N];
char str;
struct node{};
vector<int>G[N];
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);
        for(int i=1;i<=n;i++)G[i].clear(),vis[i]=0,c[i]=0;
        for(int i=1;i<=m;i++){
            scanf("%d%d",&u,&v);
            G[u].push_back(v);
            G[v].push_back(u);
        }
        sum=0;
        for(int i=1;i<=n;i++){
            if(!vis[i]){
                c[i]=1;++sum;
                vis[i]=1;
                for(int j=0,k=G[i].size();j<k;j++){
                    vis[G[i][j]]=1;
                }
            }
        }
        ans=sum<=n/2;
        cout<<(ans?sum:n-sum)<<endl;
        for(int i=1;i<=n;i++){
            if(ans==c[i])printf("%d ",i);
        }
        cout<<endl;
    }

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}