Problem p02774 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define ALL(obj) (obj).begin(), (obj).end()
#define SPEED                                                                  \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);

template <class T> using PQ = priority_queue<T>;
template <class T> using PQR = priority_queue<T, vector<T>, greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template <class T> vector<T> multivector(size_t N, T init) {
  return vector<T>(N, init);
}
template <class... T> auto multivector(size_t N, T... t) {
  return vector<decltype(multivector(t...))>(N, multivector(t...));
}
template <class T> void corner(bool flg, T hoge) {
  if (flg) {
    cout << hoge << endl;
    exit(0);
  }
}
template <class T, class U>
ostream &operator<<(ostream &o, const map<T, U> &obj) {
  o << "{";
  for (auto &x : obj)
    o << " {" << x.first << " : " << x.second << "}"
      << ",";
  o << " }";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const set<T> &obj) {
  o << "{";
  for (auto itr = obj.begin(); itr != obj.end(); ++itr)
    o << (itr != obj.begin() ? ", " : "") << *itr;
  o << "}";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const multiset<T> &obj) {
  o << "{";
  for (auto itr = obj.begin(); itr != obj.end(); ++itr)
    o << (itr != obj.begin() ? ", " : "") << *itr;
  o << "}";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const vector<T> &obj) {
  o << "{";
  for (int i = 0; i < (int)obj.size(); ++i)
    o << (i > 0 ? ", " : "") << obj[i];
  o << "}";
  return o;
}
template <class T, class U>
ostream &operator<<(ostream &o, const pair<T, U> &obj) {
  o << "{" << obj.first << ", " << obj.second << "}";
  return o;
}
void print(void) { cout << endl; }
template <class Head> void print(Head &&head) {
  cout << head;
  print();
}
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head << " ";
  print(forward<Tail>(tail)...);
}
template <class T> void chmax(T &a, const T b) { a = max(a, b); }
template <class T> void chmin(T &a, const T b) { a = min(a, b); }
void YN(bool flg) { cout << (flg ? "YES" : "NO") << endl; }
void Yn(bool flg) { cout << (flg ? "Yes" : "No") << endl; }
void yn(bool flg) { cout << (flg ? "yes" : "no") << endl; }

int main() {
  ll N, K;
  cin >> N >> K;
  vector<ll> A, B;
  for (int i = 0; i < N; ++i) {
    ll C;
    cin >> C;
    (C >= 0 ? A : B).push_back(C);
  }
  sort(ALL(A));
  sort(ALL(B));
  ll X = A.size();
  ll Y = B.size();

  ll ok = HIGHINF, ng = -HIGHINF, md;
  while (ok - ng > 1) {
    md = (ok + ng) / 2;
    ll cnt = 0;
    for (int i = 0; i + 1 < X; ++i) {
      if (A[i] * A[i + 1] > md)
        continue;
      int ok2 = i + 1, ng2 = X, md2;
      while (ng2 - ok2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (A[i] * A[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += ok2 - i;
    }
    for (int i = Y - 1; 0 <= i - 1; --i) {
      if (B[i - 1] * B[i] > md)
        continue;
      int ok2 = i - 1, ng2 = -1, md2;
      while (ok2 - ng2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (B[i] * B[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += i - ok2;
    }
    for (int i = 0; i < X; ++i) {
      if (A[i] * B[0] > md)
        continue;
      int ok2 = 0, ng2 = Y, md2;
      while (ng2 - ok2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (A[i] * B[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += ok2 + 1;
    }
    (cnt >= K ? ok : ng) = md;
  }
  cout << ok << endl;

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define ALL(obj) (obj).begin(), (obj).end()
#define SPEED                                                                  \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);

template <class T> using PQ = priority_queue<T>;
template <class T> using PQR = priority_queue<T, vector<T>, greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template <class T> vector<T> multivector(size_t N, T init) {
  return vector<T>(N, init);
}
template <class... T> auto multivector(size_t N, T... t) {
  return vector<decltype(multivector(t...))>(N, multivector(t...));
}
template <class T> void corner(bool flg, T hoge) {
  if (flg) {
    cout << hoge << endl;
    exit(0);
  }
}
template <class T, class U>
ostream &operator<<(ostream &o, const map<T, U> &obj) {
  o << "{";
  for (auto &x : obj)
    o << " {" << x.first << " : " << x.second << "}"
      << ",";
  o << " }";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const set<T> &obj) {
  o << "{";
  for (auto itr = obj.begin(); itr != obj.end(); ++itr)
    o << (itr != obj.begin() ? ", " : "") << *itr;
  o << "}";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const multiset<T> &obj) {
  o << "{";
  for (auto itr = obj.begin(); itr != obj.end(); ++itr)
    o << (itr != obj.begin() ? ", " : "") << *itr;
  o << "}";
  return o;
}
template <class T> ostream &operator<<(ostream &o, const vector<T> &obj) {
  o << "{";
  for (int i = 0; i < (int)obj.size(); ++i)
    o << (i > 0 ? ", " : "") << obj[i];
  o << "}";
  return o;
}
template <class T, class U>
ostream &operator<<(ostream &o, const pair<T, U> &obj) {
  o << "{" << obj.first << ", " << obj.second << "}";
  return o;
}
void print(void) { cout << endl; }
template <class Head> void print(Head &&head) {
  cout << head;
  print();
}
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head << " ";
  print(forward<Tail>(tail)...);
}
template <class T> void chmax(T &a, const T b) { a = max(a, b); }
template <class T> void chmin(T &a, const T b) { a = min(a, b); }
void YN(bool flg) { cout << (flg ? "YES" : "NO") << endl; }
void Yn(bool flg) { cout << (flg ? "Yes" : "No") << endl; }
void yn(bool flg) { cout << (flg ? "yes" : "no") << endl; }

int main() {
  ll N, K;
  cin >> N >> K;
  vector<ll> A, B;
  for (int i = 0; i < N; ++i) {
    ll C;
    cin >> C;
    (C >= 0 ? A : B).push_back(C);
  }
  sort(ALL(A));
  sort(ALL(B));
  ll X = A.size();
  ll Y = B.size();

  ll ok = HIGHINF, ng = -HIGHINF, md;
  while (ok - ng > 1) {
    md = (ok + ng) / 2;
    ll cnt = 0;
    for (int i = 0; i + 1 < X; ++i) {
      if (A[i] * A[i + 1] > md)
        continue;
      int ok2 = i + 1, ng2 = X, md2;
      while (ng2 - ok2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (A[i] * A[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += ok2 - i;
    }
    for (int i = Y - 1; 0 <= i - 1; --i) {
      if (B[i - 1] * B[i] > md)
        continue;
      int ok2 = i - 1, ng2 = -1, md2;
      while (ok2 - ng2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (B[i] * B[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += i - ok2;
    }
    for (int i = 0; i < X; ++i) {
      if (B.empty())
        continue;
      if (A[i] * B[0] > md)
        continue;
      int ok2 = 0, ng2 = Y, md2;
      while (ng2 - ok2 > 1) {
        md2 = (ok2 + ng2) / 2;
        (A[i] * B[md2] <= md ? ok2 : ng2) = md2;
      }
      cnt += ok2 + 1;
    }
    (cnt >= K ? ok : ng) = md;
  }
  cout << ok << endl;

  return 0;
}