Problem p02678 (C++) — buggy submission, verdict: Time Limit Exceeded

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

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;

#define repa(i, a, b) for (auto i = (a); i <= (b); i++)
#define repd(i, a, b) for (auto i = (a); i >= (b); i--)
#define rep(i, n) for (int i = 0; i < n; i++)
#define all(x) (x).begin(), (x).end()
#define zero(a) memset((a), 0, sizeof(a))
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back

constexpr auto inf = numeric_limits<int>().max();
constexpr auto llinf = numeric_limits<ll>().max();

template <typename ForwardIterator>
void dump(ForwardIterator st, ForwardIterator en) {
  for (auto it = st; it != en; it++) {
    cout << *it << " ";
  }
  cout << endl;
}

template <typename ForwardIterator>
void dump_map(ForwardIterator st, ForwardIterator en) {
  for (auto it = st; it != en; it++) {
    cout << (*it).first << ":" << (*it).second << " ";
  }
  cout << endl;
}

template <typename T> void debug(initializer_list<T> list) {
  for (auto el : list) {
    cout << el << " ";
  }
  cout << endl;
}

int n, m;
vvi adj;
constexpr int mxN = 100010;
bitset<mxN> visited;
vi parent;

void bfs(int st) {
  queue<int> q;
  q.push(st);
  while (!q.empty()) {
    auto u = q.front();
    // debug({u});
    q.pop();
    if (visited.test(u))
      continue;
    for (auto v : adj[u]) {
      if (!visited.test(v)) {
        if (parent[v] == -1) {
          parent[v] = u;
        }
        q.push(v);
      }
    }
    visited.set(u);
  }
}

void solve() {
  cin >> n >> m;
  adj.resize(n + 1);
  int a, b;
  rep(i, m) {
    cin >> a >> b;
    adj[a].pb(b);
    adj[b].pb(a);
  }
  // repa(i, 1, n) {
  // 	cout << i << ": ";
  // 	dump(all(adj[i]));
  // }
  visited.reset();
  parent.resize(n + 1);
  fill(all(parent), -1);
  bfs(1);
  if (find(parent.begin() + 2, parent.end(), -1) == parent.end()) {
    cout << "Yes\\n";
    repa(i, 2, n) { cout << parent[i] << "\\n"; }
  } else {
    cout << "No\\n";
  }
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}


Error: TLE

Fixed submission:

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

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;

#define repa(i, a, b) for (auto i = (a); i <= (b); i++)
#define repd(i, a, b) for (auto i = (a); i >= (b); i--)
#define rep(i, n) for (int i = 0; i < n; i++)
#define all(x) (x).begin(), (x).end()
#define zero(a) memset((a), 0, sizeof(a))
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back

constexpr auto inf = numeric_limits<int>().max();
constexpr auto llinf = numeric_limits<ll>().max();

template <typename ForwardIterator>
void dump(ForwardIterator st, ForwardIterator en) {
  for (auto it = st; it != en; it++) {
    cout << *it << " ";
  }
  cout << endl;
}

template <typename ForwardIterator>
void dump_map(ForwardIterator st, ForwardIterator en) {
  for (auto it = st; it != en; it++) {
    cout << (*it).first << ":" << (*it).second << " ";
  }
  cout << endl;
}

template <typename T> void debug(initializer_list<T> list) {
  for (auto el : list) {
    cout << el << " ";
  }
  cout << endl;
}

int n, m;
vvi adj;
constexpr int mxN = 100010;
bitset<mxN> visited;
vi parent;

void bfs(int st) {
  queue<int> q;
  q.push(st);
  while (!q.empty()) {
    auto u = q.front();
    // debug({u});
    q.pop();
    // if (visited.test(u)) continue;
    for (auto v : adj[u]) {
      if (!visited.test(v)) {
        if (parent[v] == -1) {
          parent[v] = u;
        }
        q.push(v);
      }
    }
    visited.set(u);
  }
}

void solve() {
  cin >> n >> m;
  adj.resize(n + 1);
  int a, b;
  rep(i, m) {
    cin >> a >> b;
    adj[a].pb(b);
    adj[b].pb(a);
  }
  // repa(i, 1, n) {
  // 	cout << i << ": ";
  // 	dump(all(adj[i]));
  // }
  visited.reset();
  parent.resize(n + 1);
  fill(all(parent), -1);
  bfs(1);
  if (find(parent.begin() + 2, parent.end(), -1) == parent.end()) {
    cout << "Yes\\n";
    repa(i, 2, n) { cout << parent[i] << "\\n"; }
  } else {
    cout << "No\\n";
  }
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}