Problem p02678 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

// 総数を1000000007（素数）で割った余り
const long long mod = 1e9 + 7;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define ull unsigned long long
#define ld long double
#define vi vector<int>
#define vll vector<ll>
#define vc vector<char>
#define vs vector<string>
#define vpii vector<pii>
#define vpll vector<pll>

#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; i++)
#define rep1(i, n) for (int i = 1, i##_len = (n); i <= i##_len; i++)
#define repr(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rep1r(i, n) for (int i = ((int)(n)); i >= 1; i--)

#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define RSORT(x) sort(rall(x));
#define pb push_back
#define mp make_pair

#define INF (1e9)
#define PI (acos(-1))
#define EPS (1e-7)

ull gcd(ull a, ull b) { return b ? gcd(b, a % b) : a; }
ull lcm(ull a, ull b) { return a / gcd(a, b) * b; }

const string YES = "Yes";

int main() {
  int n, m;
  cin >> n >> m;
  vector<vi> g(n, vi(n));
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    g[a].pb(b);
    g[b].pb(a);
  }
  queue<int> q;
  vi dir(n, INF);
  q.push(0);
  dir[0] = -1;
  while (!q.empty()) {
    int p = q.front();
    q.pop();
    for (int i : g[p]) {
      if (dir[i] != INF)
        continue;
      q.push(i);
      dir[i] = p;
    }
  }
  bool ans = true;
  rep(i, n) {
    if (dir[i] == INF)
      ans = false;
  }
  if (!ans)
    puts("No");
  else {
    puts("Yes");
    rep1(i, n - 1) cout << dir[i] + 1 << endl;
  }
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

// 総数を1000000007（素数）で割った余り
const long long mod = 1e9 + 7;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define ull unsigned long long
#define ld long double
#define vi vector<int>
#define vll vector<ll>
#define vc vector<char>
#define vs vector<string>
#define vpii vector<pii>
#define vpll vector<pll>

#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; i++)
#define rep1(i, n) for (int i = 1, i##_len = (n); i <= i##_len; i++)
#define repr(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rep1r(i, n) for (int i = ((int)(n)); i >= 1; i--)

#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define RSORT(x) sort(rall(x));
#define pb push_back
#define mp make_pair

#define INF (1e9)
#define PI (acos(-1))
#define EPS (1e-7)

ull gcd(ull a, ull b) { return b ? gcd(b, a % b) : a; }
ull lcm(ull a, ull b) { return a / gcd(a, b) * b; }

const string YES = "Yes";

int main() {
  int n, m;
  cin >> n >> m;
  vector<vi> g(n);
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    g[a].pb(b);
    g[b].pb(a);
  }
  queue<int> q;
  vi dir(n, INF);
  q.push(0);
  dir[0] = -1;
  while (!q.empty()) {
    int p = q.front();
    q.pop();
    for (int i : g[p]) {
      if (dir[i] != INF)
        continue;
      q.push(i);
      dir[i] = p;
    }
  }
  bool ans = true;
  rep(i, n) {
    if (dir[i] == INF)
      ans = false;
  }
  if (!ans)
    puts("No");
  else {
    puts("Yes");
    rep1(i, n - 1) cout << dir[i] + 1 << endl;
  }
  return 0;
}