Problem p02678 (C++)

Buggy submission (status: Runtime Error):
/* #region Head */

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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll, ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;
using vll = vc<ll>;
using vvll = vvc<ll>;
using vld = vc<ld>;
using vvld = vvc<ld>;
using vs = vc<string>;
using vvs = vvc<string>;
template <class T, class U> using um = unordered_map<T, U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqa = priority_queue<T, vc<T>, greater<T>>;
template <class T> using us = unordered_set<T>;

#define REP(i, m, n) for (ll i = (m), i##_len = (ll)(n); i < i##_len; ++(i))
#define REPM(i, m, n) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; ++(i))
#define REPR(i, m, n) for (ll i = (m), i##_min = (ll)(n); i >= i##_min; --(i))
#define REPD(i, m, n, d)                                                       \
  for (ll i = (m), i##_len = (ll)(n); i < i##_len; i += (d))
#define REPMD(i, m, n, d)                                                      \
  for (ll i = (m), i##_max = (ll)(n); i <= i##_max; i += (d))
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) begin(x), end(x)
#define SIZE(x) ((ll)(x).size())
#define PERM(c)                                                                \
  sort(ALL(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(ALL(c)))
#define UNIQ(v) v.erase(unique(ALL(v)), v.end());

#define endl '\n'
#define sqrt sqrtl
#define floor floorl
#define log2 log2l

constexpr ll INF = 1'010'000'000'000'000'017LL;
constexpr ll MOD = 1'000'000'007LL; // 1e9 + 7
constexpr ld EPS = 1e-12;
constexpr ld PI = 3.14159265358979323846;

template <typename T>
istream &operator>>(istream &is, vc<T> &vec) { // vector 入力
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, vc<T> &vec) { // vector 出力 (for dump)
  os << "{";
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "" : ", ");
  os << "}";
  return os;
}
template <typename T>
ostream &operator>>(ostream &os, vc<T> &vec) { // vector 出力 (inline)
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "\n" : " ");
  return os;
}

template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &pair_var) { // pair 入力
  is >> pair_var.first >> pair_var.second;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) { // pair 出力
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

// map, um, set, us 出力
template <class T> ostream &out_iter(ostream &os, T &map_var) {
  os << "{";
  REPI(itr, map_var) {
    os << *itr;
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  return os << "}";
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T, typename U>
ostream &operator<<(ostream &os, um<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, us<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, pq<T> &pq_var) {
  pq<T> pq_cp(pq_var);
  os << "{";
  if (!pq_cp.empty()) {
    os << pq_cp.top(), pq_cp.pop();
    while (!pq_cp.empty())
      os << ", " << pq_cp.top(), pq_cp.pop();
  }
  return os << "}";
}

// dump
#define DUMPOUT cerr
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0)
    DUMPOUT << ", ";
  dump_func(move(tail)...);
}

// chmax (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

// chmin (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

// ローカル用
#define DEBUG_

#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \
          << "    ",                                                           \
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

struct AtCoderInitialize {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;
  AtCoderInitialize() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} ATCODER_INITIALIZE;

string yes = "Yes", no = "No";
// string yes = "YES", no = "NO";
void yn(bool p) { cout << (p ? yes : no) << endl; }

/* #endregion */

/* #region Graph */

// エッジ（本来エッジは双方向だが，ここでは単方向で管理）
template <class weight_t, class flow_t> struct Edge {
  ll src;          // エッジ始点となる頂点
  ll dst;          // エッジ終点となる頂点
  weight_t weight; // 重み
  flow_t cap;
  Edge() : src(0), dst(0), weight(0) {}
  Edge(ll src, ll dst, weight_t weight) : src(src), dst(dst), weight(weight) {}
  Edge(ll src, ll dst, weight_t weight, flow_t cap)
      : src(src), dst(dst), weight(weight), cap(cap) {}
  // Edge 標準出力
  friend ostream &operator<<(ostream &os, Edge &edge) {
    os << "(" << edge.src << " -> " << edge.dst << ", " << edge.weight << ")";
    return os;
  }
};
// 同じ頂点を始点とするエッジ集合
template <class weight_t, class flow_t>
class Node : public vc<Edge<weight_t, flow_t>> {
public:
  ll idx;
  Node() : vc<Edge<weight_t, flow_t>>() {}
  // void add(int a, int b, weight_t w, flow_t cap) { this->emplace_back(a, b,
  // w, cap); };
};
// graph[i] := 頂点 i を始点とするエッジ集合
template <class weight_t, class flow_t>
class Graph : public vc<Node<weight_t, flow_t>> {
public:
  Graph() : vc<Node<weight_t, flow_t>>() {}
  Graph(int n) : vc<Node<weight_t, flow_t>>(n) {
    REP(i, 0, n)(*this)[i].idx = i;
  }
  // 単方向
  void add_arc(int a, int b, weight_t w = 1, flow_t cap = 1) {
    (*this)[a].emplace_back(a, b, w, cap);
  }
  // 双方向
  void add_edge(int a, int b, weight_t w = 1, flow_t cap = 1) {
    add_arc(a, b, w, cap), add_arc(b, a, w, cap);
  }
};
// using Array = vc<Weight>;
// using Matrix = vc<Array>;

/* #endregion */

// Problem
void solve() {
  ll n, m;
  cin >> n >> m;
  vll a(m), b(m);
  REP(i, 0, m) {
    cin >> a[i] >> b[i];
    a[i]--, b[i]--;
  }

  Graph<ll, ll> graph(n);
  REP(i, 0, n) graph.add_edge(a[i], b[i]);

  vll dist(n, -1);
  queue<Node<ll, ll>> que; // 「訪問予定」頂点リスト

  // 初期条件 (頂点 idx1 を初期頂点とする)
  dist[0] = 0;
  que.push(graph[0]); // 頂点 idx を「訪問予定」頂点リストに追加

  // BFS 開始 (キューが空になるまで探索を行う)
  while (!que.empty()) {
    Node<ll, ll> current = que.front(); // キューから先頭頂点を取り出す
    que.pop();

    // cuerrent から辿れる頂点をすべて調べる
    for (Edge<ll, ll> edge : current) {
      if (dist[edge.dst] != -1)
        continue; // 訪問済み (weight=1 固定なら continue してよい)

      // 未訪問の頂点 nv について距離情報を更新してキューに追加する
      dist[edge.dst] = edge.src;
      que.push(graph[edge.dst]);
    }
  }

  // validate
  REP(i, 1, n) if (dist[i] == -1) {
    yn(false);
    return;
  }
  yn(true);
  REP(i, 1, n) cout << (dist[i] + 1) << endl;
}

// entry point
int main() {
  solve();
  return 0;
}


Fixed submission:
/* #region Head */

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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll, ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;
using vll = vc<ll>;
using vvll = vvc<ll>;
using vld = vc<ld>;
using vvld = vvc<ld>;
using vs = vc<string>;
using vvs = vvc<string>;
template <class T, class U> using um = unordered_map<T, U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqa = priority_queue<T, vc<T>, greater<T>>;
template <class T> using us = unordered_set<T>;

#define REP(i, m, n) for (ll i = (m), i##_len = (ll)(n); i < i##_len; ++(i))
#define REPM(i, m, n) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; ++(i))
#define REPR(i, m, n) for (ll i = (m), i##_min = (ll)(n); i >= i##_min; --(i))
#define REPD(i, m, n, d)                                                       \
  for (ll i = (m), i##_len = (ll)(n); i < i##_len; i += (d))
#define REPMD(i, m, n, d)                                                      \
  for (ll i = (m), i##_max = (ll)(n); i <= i##_max; i += (d))
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define ALL(x) begin(x), end(x)
#define SIZE(x) ((ll)(x).size())
#define PERM(c)                                                                \
  sort(ALL(c));                                                                \
  for (bool c##p = 1; c##p; c##p = next_permutation(ALL(c)))
#define UNIQ(v) v.erase(unique(ALL(v)), v.end());

#define endl '\n'
#define sqrt sqrtl
#define floor floorl
#define log2 log2l

constexpr ll INF = 1'010'000'000'000'000'017LL;
constexpr ll MOD = 1'000'000'007LL; // 1e9 + 7
constexpr ld EPS = 1e-12;
constexpr ld PI = 3.14159265358979323846;

template <typename T>
istream &operator>>(istream &is, vc<T> &vec) { // vector 入力
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, vc<T> &vec) { // vector 出力 (for dump)
  os << "{";
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "" : ", ");
  os << "}";
  return os;
}
template <typename T>
ostream &operator>>(ostream &os, vc<T> &vec) { // vector 出力 (inline)
  REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "\n" : " ");
  return os;
}

template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &pair_var) { // pair 入力
  is >> pair_var.first >> pair_var.second;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) { // pair 出力
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

// map, um, set, us 出力
template <class T> ostream &out_iter(ostream &os, T &map_var) {
  os << "{";
  REPI(itr, map_var) {
    os << *itr;
    auto itrcp = itr;
    if (++itrcp != map_var.end())
      os << ", ";
  }
  return os << "}";
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T, typename U>
ostream &operator<<(ostream &os, um<T, U> &map_var) {
  return out_iter(os, map_var);
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, us<T> &set_var) {
  return out_iter(os, set_var);
}
template <typename T> ostream &operator<<(ostream &os, pq<T> &pq_var) {
  pq<T> pq_cp(pq_var);
  os << "{";
  if (!pq_cp.empty()) {
    os << pq_cp.top(), pq_cp.pop();
    while (!pq_cp.empty())
      os << ", " << pq_cp.top(), pq_cp.pop();
  }
  return os << "}";
}

// dump
#define DUMPOUT cerr
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0)
    DUMPOUT << ", ";
  dump_func(move(tail)...);
}

// chmax (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmax(T &xmax, const U &x, Comp comp = {}) {
  if (comp(xmax, x)) {
    xmax = x;
    return true;
  }
  return false;
}

// chmin (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>>
bool chmin(T &xmin, const U &x, Comp comp = {}) {
  if (comp(x, xmin)) {
    xmin = x;
    return true;
  }
  return false;
}

// ローカル用
#define DEBUG_

#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \
          << "    ",                                                           \
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

struct AtCoderInitialize {
  static constexpr int IOS_PREC = 15;
  static constexpr bool AUTOFLUSH = false;
  AtCoderInitialize() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    cout << fixed << setprecision(IOS_PREC);
    if (AUTOFLUSH)
      cout << unitbuf;
  }
} ATCODER_INITIALIZE;

string yes = "Yes", no = "No";
// string yes = "YES", no = "NO";
void yn(bool p) { cout << (p ? yes : no) << endl; }

/* #endregion */

/* #region Graph */

// エッジ（本来エッジは双方向だが，ここでは単方向で管理）
template <class weight_t, class flow_t> struct Edge {
  ll src;          // エッジ始点となる頂点
  ll dst;          // エッジ終点となる頂点
  weight_t weight; // 重み
  flow_t cap;
  Edge() : src(0), dst(0), weight(0) {}
  Edge(ll src, ll dst, weight_t weight) : src(src), dst(dst), weight(weight) {}
  Edge(ll src, ll dst, weight_t weight, flow_t cap)
      : src(src), dst(dst), weight(weight), cap(cap) {}
  // Edge 標準出力
  friend ostream &operator<<(ostream &os, Edge &edge) {
    os << "(" << edge.src << " -> " << edge.dst << ", " << edge.weight << ")";
    return os;
  }
};
// 同じ頂点を始点とするエッジ集合
template <class weight_t, class flow_t>
class Node : public vc<Edge<weight_t, flow_t>> {
public:
  ll idx;
  Node() : vc<Edge<weight_t, flow_t>>() {}
  // void add(int a, int b, weight_t w, flow_t cap) { this->emplace_back(a, b,
  // w, cap); };
};
// graph[i] := 頂点 i を始点とするエッジ集合
template <class weight_t, class flow_t>
class Graph : public vc<Node<weight_t, flow_t>> {
public:
  Graph() : vc<Node<weight_t, flow_t>>() {}
  Graph(int n) : vc<Node<weight_t, flow_t>>(n) {
    REP(i, 0, n)(*this)[i].idx = i;
  }
  // 単方向
  void add_arc(int a, int b, weight_t w = 1, flow_t cap = 1) {
    (*this)[a].emplace_back(a, b, w, cap);
  }
  // 双方向
  void add_edge(int a, int b, weight_t w = 1, flow_t cap = 1) {
    add_arc(a, b, w, cap), add_arc(b, a, w, cap);
  }
};
// using Array = vc<Weight>;
// using Matrix = vc<Array>;

/* #endregion */

// Problem
void solve() {
  ll n, m;
  cin >> n >> m;
  vll a(m), b(m);
  REP(i, 0, m) {
    cin >> a[i] >> b[i];
    a[i]--, b[i]--;
  }

  Graph<ll, ll> graph(n);
  REP(i, 0, m) graph.add_edge(a[i], b[i]);

  vll dist(n, -1);
  queue<Node<ll, ll>> que; // 「訪問予定」頂点リスト

  // 初期条件 (頂点 idx1 を初期頂点とする)
  dist[0] = 0;
  que.push(graph[0]); // 頂点 idx を「訪問予定」頂点リストに追加

  // BFS 開始 (キューが空になるまで探索を行う)
  while (!que.empty()) {
    Node<ll, ll> current = que.front(); // キューから先頭頂点を取り出す
    que.pop();

    // cuerrent から辿れる頂点をすべて調べる
    for (Edge<ll, ll> edge : current) {
      if (dist[edge.dst] != -1)
        continue; // 訪問済み (weight=1 固定なら continue してよい)

      // 未訪問の頂点 nv について距離情報を更新してキューに追加する
      dist[edge.dst] = edge.src;
      que.push(graph[edge.dst]);
    }
  }

  // validate
  REP(i, 1, n) if (dist[i] == -1) {
    yn(false);
    return;
  }
  yn(true);
  REP(i, 1, n) cout << (dist[i] + 1) << endl;
}

// entry point
int main() {
  solve();
  return 0;
}