Problem p02616 (C++)

Buggy submission (status: Runtime Error):
#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
// #pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<char> Vc;
typedef vector<P> VP;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;
typedef vector<vector<char>> VVc;
typedef vector<vector<vector<ll>>> VVV;
typedef vector<vector<vector<vector<ll>>>> VVVV;

#define REP(i, a, b) for (ll i = (a); i < (b); i++)
#define PER(i, a, b) for (ll i = (a); i >= (b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF = 1e18 + 18;
const ll MOD = 1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define rALL(v) v.rbegin(), v.rend()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a, b)
#define Each(a, b) for (auto &a : b)
#define rEach(i, mp) for (auto i = mp.rbegin(); i != mp.rend(); ++i)
#ifdef LOCAL
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp)                                                             \
  cerr << #mp << ":" << endl;                                                  \
  for (auto i = mp.begin(); i != mp.end(); ++i) {                              \
    cerr << i->first << ":" << i->second << endl;                              \
  }
#define dbgset(st)                                                             \
  cerr << #st << ":" << endl;                                                  \
  for (auto i = st.begin(); i != st.end(); ++i) {                              \
    cerr << *i << " ";                                                         \
  }                                                                            \
  cerr << endl;
#define dbgarr(n, m, arr)                                                      \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j] << " "; }                                    \
    cerr << endl;                                                              \
  }
#define dbgdp(n, arr)                                                          \
  rep(i, n) { cerr << arr[i] << " "; }                                         \
  cerr << endl;
#define dbgmint(n, arr)                                                        \
  rep(i, n) { cerr << arr[i].x << " "; }                                       \
  cerr << endl;
#define dbgarrmint(n, m, arr)                                                  \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j].x << " "; }                                  \
    cerr << endl;                                                              \
  }
#else
#define dbg(...)
#define dbgmap(...)
#define dbgset(...)
#define dbgarr(...)
#define dbgdp(...)
#define dbgmint(...)
#define dbgarrmint(...)
#endif
#define out(a) cout << a << endl
#define out2(a, b) cout << a << " " << b << endl
#define vout(v)                                                                \
  rep(i, v.size()) { cout << v[i] << " "; }                                    \
  cout << endl
#define Uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define fi first
#define se second

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

template <typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}

template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, v.size()) i >> v[j];
  return i;
}

// vector
template <typename T> ostream &operator<<(ostream &s, const vector<T> &v) {
  int len = v.size();
  for (int i = 0; i < len; ++i) {
    s << v[i];
    if (i < len - 1)
      s << "	";
  }
  return s;
}

// 2 dimentional vector
template <typename T>
ostream &operator<<(ostream &s, const vector<vector<T>> &vv) {
  int len = vv.size();
  for (int i = 0; i < len; ++i) {
    s << vv[i] << endl;
  }
  return s;
}

// mint
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % MOD + MOD) % MOD) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= MOD;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime MOD
  mint inv() const { return pow(MOD - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
typedef vector<mint> Vmint;

struct combination {
  vector<mint> fact, ifact;
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < MOD);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};

int solve() {
  ll n, k;
  cin >> n >> k;
  Vec a(n);
  cin >> a;
  Vec plus;
  Vec minus;
  ll zero = 0;
  if (k == n) {
    mint ans = 1;
    rep(i, n) { ans *= a[i]; }
    out(ans);
    return 0;
  }
  if (k == 1) {
    ll ans = -INF;
    rep(i, n) { chmax(ans, a[i]); }
    out(ans);
    return 0;
  }

  deque<ll> pq;
  deque<ll> mq;
  rep(i, n) {
    if (a[i] > 0) {
      plus.pb(a[i]);
    } else if (a[i] == 0) {
      zero++;
    } else {
      minus.pb(-a[i]);
    }
  }

  sort(rALL(plus));
  sort(rALL(minus));
  dbg(plus);
  dbg(minus);

  // 絶望ストップロス
  if (zero == 0 && plus.empty() && k % 2 == 1) {
    sort(ALL(minus));
    mint ans = 1;
    rep(i, k) { ans *= -minus[i]; }
    out(ans);
    return 0;
  }

  if (plus.empty() && k % 2 == 1) {
    if (zero > 0) {
      out(0);
      return 0;
    }
  }

  ll plable = plus.size();
  ll miable = minus.size() / 2 * 2;

  // 不等号変更した
  if (k % 2 == 1 && k - (plable + miable) <= 2) {
    mint ans = 1;
    rep(i, miable) { ans *= minus[i]; }
    k -= miable;
    if (plus.size() >= k) {
      rep(i, k) { ans *= plus[i]; }
      out(ans);
    } else {
      if (zero > 0) {
        out(0);
      } else {
        ll x = 3LL / 0;
        exit(15);
      }
    }
    return 0;
  }

  mint ans = 1;

  rep(i, plus.size()) { pq.push_back(plus[i]); }
  rep(i, minus.size()) { mq.push_back(minus[i]); }
  while (k) {
    dbg(k);
    if (k == 1) {
      // 場合分け
      if (!pq.empty()) {
        ans *= pq[0];
        k--;
        break;
      } else {
        if (zero > 0) {
          out(0);
          exit(0);
        } else {
          ans *= mq[0];
          k--;
          break;
        }
      }
    } else {
      ll pp = -INF;
      ll mm = -INF;
      if (pq.size() >= 2) {
        pp = pq[0] * pq[1];
      }
      if (mq.size() >= 2) {
        mm = mq[0] * mq[1];
      }

      if (pp == -INF && mm == -INF) {
        out(0);
        exit(0);
      }

      dbg(mp(pq.size(), mq.size()));
      if (pp > mm) {
        ans *= pq[0] * pq[1];
        pq.pop_front();
        pq.pop_front();
      } else {
        ans *= mq[0] * mq[1];
        mq.pop_front();
        mq.pop_front();
      }
      dbg(mp(pp, mm));
      k -= 2;
    }
  }
  out(ans);
  return 0;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);
  solve();
}


Fixed submission:
#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
// #pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<char> Vc;
typedef vector<P> VP;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;
typedef vector<vector<char>> VVc;
typedef vector<vector<vector<ll>>> VVV;
typedef vector<vector<vector<vector<ll>>>> VVVV;

#define REP(i, a, b) for (ll i = (a); i < (b); i++)
#define PER(i, a, b) for (ll i = (a); i >= (b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF = 1e18 + 18;
const ll MOD = 1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define rALL(v) v.rbegin(), v.rend()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a, b)
#define Each(a, b) for (auto &a : b)
#define rEach(i, mp) for (auto i = mp.rbegin(); i != mp.rend(); ++i)
#ifdef LOCAL
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp)                                                             \
  cerr << #mp << ":" << endl;                                                  \
  for (auto i = mp.begin(); i != mp.end(); ++i) {                              \
    cerr << i->first << ":" << i->second << endl;                              \
  }
#define dbgset(st)                                                             \
  cerr << #st << ":" << endl;                                                  \
  for (auto i = st.begin(); i != st.end(); ++i) {                              \
    cerr << *i << " ";                                                         \
  }                                                                            \
  cerr << endl;
#define dbgarr(n, m, arr)                                                      \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j] << " "; }                                    \
    cerr << endl;                                                              \
  }
#define dbgdp(n, arr)                                                          \
  rep(i, n) { cerr << arr[i] << " "; }                                         \
  cerr << endl;
#define dbgmint(n, arr)                                                        \
  rep(i, n) { cerr << arr[i].x << " "; }                                       \
  cerr << endl;
#define dbgarrmint(n, m, arr)                                                  \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j].x << " "; }                                  \
    cerr << endl;                                                              \
  }
#else
#define dbg(...)
#define dbgmap(...)
#define dbgset(...)
#define dbgarr(...)
#define dbgdp(...)
#define dbgmint(...)
#define dbgarrmint(...)
#endif
#define out(a) cout << a << endl
#define out2(a, b) cout << a << " " << b << endl
#define vout(v)                                                                \
  rep(i, v.size()) { cout << v[i] << " "; }                                    \
  cout << endl
#define Uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define fi first
#define se second

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

template <typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}

template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, v.size()) i >> v[j];
  return i;
}

// vector
template <typename T> ostream &operator<<(ostream &s, const vector<T> &v) {
  int len = v.size();
  for (int i = 0; i < len; ++i) {
    s << v[i];
    if (i < len - 1)
      s << "	";
  }
  return s;
}

// 2 dimentional vector
template <typename T>
ostream &operator<<(ostream &s, const vector<vector<T>> &vv) {
  int len = vv.size();
  for (int i = 0; i < len; ++i) {
    s << vv[i] << endl;
  }
  return s;
}

// mint
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % MOD + MOD) % MOD) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += MOD - a.x) >= MOD)
      x -= MOD;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= MOD;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime MOD
  mint inv() const { return pow(MOD - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
typedef vector<mint> Vmint;

struct combination {
  vector<mint> fact, ifact;
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < MOD);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i)
      fact[i] = fact[i - 1] * i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i)
      ifact[i - 1] = ifact[i] * i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};

int solve() {
  ll n, k;
  cin >> n >> k;
  Vec a(n);
  cin >> a;
  Vec plus;
  Vec minus;
  ll zero = 0;
  if (k == n) {
    mint ans = 1;
    rep(i, n) { ans *= a[i]; }
    out(ans);
    return 0;
  }
  if (k == 1) {
    ll ans = -INF;
    rep(i, n) { chmax(ans, a[i]); }
    out(ans);
    return 0;
  }

  deque<ll> pq;
  deque<ll> mq;
  rep(i, n) {
    if (a[i] > 0) {
      plus.pb(a[i]);
    } else if (a[i] == 0) {
      zero++;
    } else {
      minus.pb(-a[i]);
    }
  }

  sort(rALL(plus));
  sort(rALL(minus));
  dbg(plus);
  dbg(minus);

  // 絶望ストップロス
  if (zero == 0 && plus.empty() && k % 2 == 1) {
    sort(ALL(minus));
    mint ans = 1;
    rep(i, k) { ans *= -minus[i]; }
    out(ans);
    return 0;
  }

  if (plus.empty() && k % 2 == 1) {
    if (zero > 0) {
      out(0);
      return 0;
    }
  }

  ll plable = plus.size();
  ll miable = minus.size() / 2 * 2;

  // 不等号変更した
  if (k % 2 == 1 && (plable + miable) - k < 2) {
    mint ans = 1;
    rep(i, miable) { ans *= minus[i]; }
    k -= miable;
    if (plus.size() >= k) {
      rep(i, k) { ans *= plus[i]; }
      out(ans);
    } else {
      if (zero > 0) {
        out(0);
      } else {
        ll x = 3LL / 0;
        exit(15);
      }
    }
    return 0;
  }

  mint ans = 1;

  rep(i, plus.size()) { pq.push_back(plus[i]); }
  rep(i, minus.size()) { mq.push_back(minus[i]); }
  while (k) {
    dbg(k);
    if (k == 1) {
      // 場合分け
      if (!pq.empty()) {
        ans *= pq[0];
        k--;
        break;
      } else {
        if (zero > 0) {
          out(0);
          exit(0);
        } else {
          ans *= mq[0];
          k--;
          break;
        }
      }
    } else {
      ll pp = -INF;
      ll mm = -INF;
      if (pq.size() >= 2) {
        pp = pq[0] * pq[1];
      }
      if (mq.size() >= 2) {
        mm = mq[0] * mq[1];
      }

      if (pp == -INF && mm == -INF) {
        out(0);
        exit(0);
      }

      dbg(mp(pq.size(), mq.size()));
      if (pp > mm) {
        ans *= pq[0] * pq[1];
        pq.pop_front();
        pq.pop_front();
      } else {
        ans *= mq[0] * mq[1];
        mq.pop_front();
        mq.pop_front();
      }
      dbg(mp(pp, mm));
      k -= 2;
    }
  }
  out(ans);
  return 0;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);
  solve();
}