https://codeforces.com/contest/1133/problem/F1

题解：贪心+并查集

首先统计每个节点的度的数量，按度的数量从大到小排序，然后并查集建树（类似于最小生成树）

C++版本一

/*
*@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
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,q;
int ans,cnt,flag,temp,sum,u,v;
int a[N];
int pre[N];
char str;
vector<int>G[N];
struct node{
    int a,id;
    bool operator<(const node &S)const{
        if(a==S.a)
            return id<S.id;
        return a>S.a;
    }
}e[N];
int find(int x){return (pre[x]==x)?x:pre[x]=find(pre[x]);}
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++){
        e[i].id=i;
        pre[i]=i;
    }

    for(int i=1;i<=m;i++){
        scanf("%d%d",&u,&v);
        e[u].a++;
        e[v].a++;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    sort(e+1,e+n+1);
    for(int i=1;i<=n;i++){
        for(int j=0,k=G[e[i].id].size();j<k;j++){
            u=e[i].id;
            v=G[e[i].id][j];
            int tx=find(u);
            int ty=find(v);
            if(tx!=ty){
                pre[tx]=ty;
                cout<<u<<" "<<v<<endl;
            }
        }
    }
    //}

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