Codeforces Round #544 (Div. 3) F1. Spanning Tree with Maximum Degree(bfs)

#include <bits/stdc++.h>
#define ll long long
#define maxn 200005
using namespace std;
int n,m;
vector<int> v[maxn];
int pos, cnt;

void bfs(){
  queue<int> q;
  bool vis[maxn];
  memset(vis,false,sizeof(vis));
  q.push(pos);
  vis[pos] = true;
  while(!q.empty()){
    int u = q.front();
    q.pop();
    for(int i=0;i<v[u].size();i++){
      if(vis[v[u][i]] == false){
        vis[v[u][i]] = true;
        printf("%d %d\n", u, v[u][i]);
        q.push(v[u][i]);
      }
    }
  }
}

int main()
{
  scanf("%d%d",&n,&m);
  cnt = 0;
  for(int i=0;i<m;i++){
    int x,y;
    scanf("%d%d",&x,&y);
    v[x].push_back(y);
    v[y].push_back(x);
    if(cnt < v[x].size()){
      cnt = v[x].size();
      pos = x;
    }
    if(cnt < v[y].size()){
      cnt = v[y].size();
      pos = y;
    }
  }
  bfs();
  return 0;
}