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

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define mk make_pair
#define fi first
#define se second
#define vll vector<ll>
#define pii pair<ll, ll>
#define vvll vector<vector<ll>>
#define pb push_back
#define sz(v) (v).size()
#define inf 1e18
#define md 1000000007
#define all(v) (v).begin(), (v).end()
#define rep(i, a, b) for (ll i = a; i < b; ++i)
#define tel(a)                                                                 \\
  { cout << a << "\\n"; }
#define tell(a, b)                                                             \\
  { cout << a << " | " << b << "\\n"; }
#define telll(a, b, c)                                                         \\
  { cout << a << " | " << b << " | " << c << "\\n"; }
#define teln(v, n)                                                             \\
  {                                                                            \\
    cout << "v- ";                                                             \\
    rep(o, 0, n) cout << v[o] << " ";                                          \\
    cout << "\\n";                                                              \\
  }
#define IOS                                                                    \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define tihs                                                                   \\
  if (fopen("inp.txt", "r"))                                                   \\
    freopen("inp.txt", "r", stdin), freopen("out.txt", "w", stdout);
using namespace std;
#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

#define M 100010
vll g[M];
ll p[M], lev[M];

int main() {
  IOS;
  tihs;

  ll n, m;
  cin >> n >> m;
  rep(i, 0, m) {
    ll u, v;
    cin >> u >> v;
    u--, v--;
    g[u].pb(v), g[v].pb(u);
  }
  rep(i, 0, n) lev[i] = -1, p[i] = i;
  lev[0] = 0;
  queue<ll> q;
  q.push(0);
  while (!q.empty()) {
    ll u = q.front();
    q.pop();
    for (auto v : g[u])
      if (lev[v] == -1)
        lev[v] = lev[u] + 1, p[v] = u, q.push(v);
  }
  cout << "Yes\\n";
  rep(i, 1, n) cout << p[i] + 1 << "\\n";

  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define mk make_pair
#define fi first
#define se second
#define vll vector<ll>
#define pii pair<ll, ll>
#define vvll vector<vector<ll>>
#define pb push_back
#define sz(v) (v).size()
#define inf 1e18
#define md 1000000007
#define all(v) (v).begin(), (v).end()
#define rep(i, a, b) for (ll i = a; i < b; ++i)
#define tel(a)                                                                 \\
  { cout << a << "\\n"; }
#define tell(a, b)                                                             \\
  { cout << a << " | " << b << "\\n"; }
#define telll(a, b, c)                                                         \\
  { cout << a << " | " << b << " | " << c << "\\n"; }
#define teln(v, n)                                                             \\
  {                                                                            \\
    cout << "v- ";                                                             \\
    rep(o, 0, n) cout << v[o] << " ";                                          \\
    cout << "\\n";                                                              \\
  }
#define IOS                                                                    \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define tihs                                                                   \\
  if (fopen("inp.txt", "r"))                                                   \\
    freopen("inp.txt", "r", stdin), freopen("out.txt", "w", stdout);
using namespace std;
#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
#else
#define trace(...)
#endif

#define M 1000010
vll g[M];
ll p[M], lev[M];
void dfs(ll u) {
  for (auto v : g[u]) {
    if (lev[v] != -1) {
      if (lev[v] <= lev[u] + 1)
        continue;
    }
    lev[v] = lev[u] + 1;
    p[v] = u;
    dfs(v);
  }
}
int main() {
  IOS;
  tihs;

  ll n, m;
  cin >> n >> m;
  rep(i, 0, m) {
    ll u, v;
    cin >> u >> v;
    u--, v--;
    g[u].pb(v), g[v].pb(u);
  }
  rep(i, 0, n) lev[i] = -1, p[i] = i;
  lev[0] = 0;
  dfs(0);
  cout << "Yes\\n";
  rep(i, 1, n) cout << p[i] + 1 << "\\n";

  return 0;
}