Problem p03685 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (ll i = int(m); i < int(n); ++i)
#define drep2(i, m, n) for (ll i = int(m) - 1; i >= int(n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) a.begin(), a.end()
struct fast_ios {
  fast_ios() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << " ";
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int Log2(ll x) {
  int k;
  for (k = 0; x > 0; ++k)
    x >>= 1;
  return k;
} // number of binary digits
const int INF = 1 << 30;
const ll INFll = 1ll << 62;
const ld EPS = 1e-10;
const int MOD = int(1e9) + 7;

int main() {
  ll r, c, n;
  cin >> r >> c >> n;

  vector<vector<P>> p(4, vector<P>());

  rep(i, n) {
    V x(2), y(2);
    Vbo b(2);
    rep(j, 2) {
      cin >> x[j] >> y[j];
      b[j] = (x[j] == 0 || x[j] == r || y[j] == 0 || y[j] == c);
    }
    if (!(b[0] && b[1]))
      continue;
    rep(j, 2) {
      if (x[j] < r && y[j] == 0)
        p[0].emplace_back(x[j], i);
      if (x[j] == r && y[j] < c)
        p[1].emplace_back(y[j], i);
      if (x[j] > 0 && y[j] == c)
        p[2].emplace_back(x[j], i);
      if (x[j] == 0 && y[j] > 0)
        p[4].emplace_back(y[j], i);
    }
  }

  sort(all(p[0]));
  sort(all(p[1]));
  sort(all(p[2]), greater<P>());
  sort(all(p[3]), greater<P>());

  stack<int> st;
  Vbo seen(n, false);

  rep(i, 4) for (auto &e : p[i]) {
    int k = e.second;
    if (seen[k]) {
      if (st.top() == k) {
        st.pop();
      } else {
        cout << "NO"
             << "\n";
        return 0;
      }
    } else {
      st.push(k);
      seen[k] = true;
    }
  }

  cout << "YES"
       << "\n";
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using V = vector<int>;
using Vll = vector<ll>;
using Vld = vector<ld>;
using Vbo = vector<bool>;
using VV = vector<V>;
using VVll = vector<Vll>;
using VVld = vector<Vld>;
using VVbo = vector<Vbo>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using Pld = pair<ld, ld>;
#define rep2(i, m, n) for (ll i = int(m); i < int(n); ++i)
#define drep2(i, m, n) for (ll i = int(m) - 1; i >= int(n); --i)
#define rep(i, n) rep2(i, 0, n)
#define drep(i, n) drep2(i, n, 0)
#define all(a) a.begin(), a.end()
struct fast_ios {
  fast_ios() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &e : v)
    is >> e;
  return is;
}
template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  for (auto &e : v)
    os << e << " ";
  return os;
}
template <typename T> inline int count_between(vector<T> &a, T l, T r) {
  return lower_bound(all(a), r) - lower_bound(all(a), l);
} // [l, r)
inline int Log2(ll x) {
  int k;
  for (k = 0; x > 0; ++k)
    x >>= 1;
  return k;
} // number of binary digits
const int INF = 1 << 30;
const ll INFll = 1ll << 62;
const ld EPS = 1e-10;
const int MOD = int(1e9) + 7;

int main() {
  ll r, c, n;
  cin >> r >> c >> n;

  vector<vector<P>> p(4, vector<P>());

  rep(i, n) {
    V x(2), y(2);
    Vbo b(2);
    rep(j, 2) {
      cin >> x[j] >> y[j];
      b[j] = (x[j] == 0 || x[j] == r || y[j] == 0 || y[j] == c);
    }
    if (b[0] && b[1])
      rep(j, 2) {
        if (x[j] < r && y[j] == 0)
          p[0].emplace_back(x[j], i);
        if (x[j] == r && y[j] < c)
          p[1].emplace_back(y[j], i);
        if (x[j] > 0 && y[j] == c)
          p[2].emplace_back(x[j], i);
        if (x[j] == 0 && y[j] > 0)
          p[3].emplace_back(y[j], i);
      }
  }

  sort(all(p[0]));
  sort(all(p[1]));
  sort(all(p[2]), greater<P>());
  sort(all(p[3]), greater<P>());

  stack<int> st;
  Vbo seen(n, false);

  rep(i, 4) for (auto &e : p[i]) {
    int k = e.second;
    if (seen[k]) {
      if (st.top() == k) {
        st.pop();
      } else {
        cout << "NO"
             << "\n";
        return 0;
      }
    } else {
      st.push(k);
      seen[k] = true;
    }
  }

  cout << "YES"
       << "\n";
  return 0;
}