Problem p02925 (C++)

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

#define ALL(a) (a).begin(), (a).end()
#define ALLR(a) (a).rbegin(), (a).rend()
#define spa << " " <<
#define lfs << fixed << setprecision(10) <<
#define test cout << "test" << endl;
#define fi first
#define se second
#define MP make_pair
#define rep(i, n, m) for (ll i = n; i < (ll)(m); i++)
#define rrep(i, n, m) for (ll i = n - 1; i >= (ll)(m); i--)
typedef long long ll;
typedef long double ld;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template <typename T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}
template <typename T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}
void pmod(ll &a, ll b) { a = (a + b) % MOD; }
void pmod(ll &a, ll b, ll c) { a = (b + c) % MOD; }
void qmod(ll &a, ll b) { a = (a * b) % MOD; }
void qmod(ll &a, ll b, ll c) { a = (b * c) % MOD; }
ll median(ll a, ll b, ll c) {
  return a + b + c - max({a, b, c}) - min({a, b, c});
}
void ans1(bool x) {
  if (x)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
void ans2(bool x) {
  if (x)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void ans3(bool x) {
  if (x)
    cout << "Yay!" << endl;
  else
    cout << ":(" << endl;
}
template <typename T1, typename T2> void ans(bool x, T1 y, T2 z) {
  if (x)
    cout << y << endl;
  else
    cout << z << endl;
}
template <typename T> void debug(vector<vector<T>> v, ll h, ll w) {
  for (ll i = 0; i < h; i++) {
    cout << v[i][0];
    for (ll j = 1; j < w; j++)
      cout spa v[i][j];
    cout << endl;
  }
};
void debug(vector<string> v, ll h, ll w) {
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++)
      cout << v[i][j];
    cout << endl;
  }
};
template <typename T> void debug(vector<T> v, ll n) {
  cout << v[0];
  for (ll i = 1; i < n; i++)
    cout spa v[i];
  cout << endl;
};
template <typename T> vector<vector<T>> vec(ll x, ll y, T w) {
  vector<vector<T>> v(x, vector<T>(y, w));
  return v;
}
ll gcd(ll x, ll y) {
  ll r;
  while (y != 0 && (r = x % y) != 0) {
    x = y;
    y = r;
  }
  return y == 0 ? x : y;
}
template <typename T> void emp(map<T, ll> &m, T x) {
  m.emplace(x, 0).first->second++;
}

int main() {
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res = 0, res1 = INF, res2 = -INF, buf = 0;
  bool judge = true;
  ll n;
  cin >> n;
  vector<queue<ll>> q(n);
  rep(i, 0, n) {
    rep(j, 0, n - 1) {
      ll x;
      cin >> x;
      x--;
      q[i].push(x);
    }
  }
  queue<ll> a;
  rep(i, 0, n) a.push(i);
  a.push(-1);
  ll cnt = 0;
  vector<ll> t(n, -1);
  while (!a.empty()) {
    ll x = a.front();
    if (x == -1) {
      if (a.size() != 1)
        a.push(-1);
      cnt++;
      a.pop();
    } else {
      ll y = -1;
      if (!q[x].empty())
        y = q[x].front();
      ll z = -2;
      if (y != -1 && !q[y].empty())
        z = q[y].front();
      if (x == z && t[x] != cnt && t[y] != cnt) {
        q[x].pop();
        q[y].pop();
        t[x] = cnt;
        t[y] = cnt;
        if (!q[x].empty())
          a.push(x);
        if (!q[y].empty())
          a.push(y);
      } else if (x == z) {
        a.push(x);
      }
      a.pop();
    }
  }
  rep(i, 0, n) {
    if (q[i].size() != 0)
      judge = false;
  }
  if (judge)
    cout << cnt << endl;
  else
    cout << -1 << endl;
  return 0;
}

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

#define ALL(a) (a).begin(), (a).end()
#define ALLR(a) (a).rbegin(), (a).rend()
#define spa << " " <<
#define lfs << fixed << setprecision(10) <<
#define test cout << "test" << endl;
#define fi first
#define se second
#define MP make_pair
#define rep(i, n, m) for (ll i = n; i < (ll)(m); i++)
#define rrep(i, n, m) for (ll i = n - 1; i >= (ll)(m); i--)
typedef long long ll;
typedef long double ld;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template <typename T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}
template <typename T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}
void pmod(ll &a, ll b) { a = (a + b) % MOD; }
void pmod(ll &a, ll b, ll c) { a = (b + c) % MOD; }
void qmod(ll &a, ll b) { a = (a * b) % MOD; }
void qmod(ll &a, ll b, ll c) { a = (b * c) % MOD; }
ll median(ll a, ll b, ll c) {
  return a + b + c - max({a, b, c}) - min({a, b, c});
}
void ans1(bool x) {
  if (x)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
void ans2(bool x) {
  if (x)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void ans3(bool x) {
  if (x)
    cout << "Yay!" << endl;
  else
    cout << ":(" << endl;
}
template <typename T1, typename T2> void ans(bool x, T1 y, T2 z) {
  if (x)
    cout << y << endl;
  else
    cout << z << endl;
}
template <typename T> void debug(vector<vector<T>> v, ll h, ll w) {
  for (ll i = 0; i < h; i++) {
    cout << v[i][0];
    for (ll j = 1; j < w; j++)
      cout spa v[i][j];
    cout << endl;
  }
};
void debug(vector<string> v, ll h, ll w) {
  for (ll i = 0; i < h; i++) {
    for (ll j = 0; j < w; j++)
      cout << v[i][j];
    cout << endl;
  }
};
template <typename T> void debug(vector<T> v, ll n) {
  cout << v[0];
  for (ll i = 1; i < n; i++)
    cout spa v[i];
  cout << endl;
};
template <typename T> vector<vector<T>> vec(ll x, ll y, T w) {
  vector<vector<T>> v(x, vector<T>(y, w));
  return v;
}
ll gcd(ll x, ll y) {
  ll r;
  while (y != 0 && (r = x % y) != 0) {
    x = y;
    y = r;
  }
  return y == 0 ? x : y;
}
template <typename T> void emp(map<T, ll> &m, T x) {
  m.emplace(x, 0).first->second++;
}

int main() {
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res = 0, res1 = INF, res2 = -INF, buf = 0;
  bool judge = true;
  ll n;
  cin >> n;
  vector<queue<ll>> q(n);
  rep(i, 0, n) {
    rep(j, 0, n - 1) {
      ll x;
      cin >> x;
      x--;
      q[i].push(x);
    }
  }
  queue<ll> a;
  rep(i, 0, n) a.push(i);
  a.push(-1);
  ll cnt = 0;
  vector<ll> t(n, -1);
  while (!a.empty()) {
    ll x = a.front();
    if (x == -1) {
      if (a.size() != 1)
        a.push(-1);
      cnt++;
      a.pop();
    } else {
      ll y = -1;
      if (!q[x].empty())
        y = q[x].front();
      ll z = -2;
      if (y != -1 && !q[y].empty())
        z = q[y].front();
      if (x == z && t[x] != cnt && t[y] != cnt) {
        q[x].pop();
        q[y].pop();
        t[x] = cnt;
        t[y] = cnt;
        if (!q[x].empty())
          a.push(x);
        if (!q[y].empty())
          a.push(y);
      }
      a.pop();
    }
  }
  rep(i, 0, n) {
    if (q[i].size() != 0)
      judge = false;
  }
  if (judge)
    cout << cnt << endl;
  else
    cout << -1 << endl;
  return 0;
}