Problem p02616 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pli pair<ll, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\n'
const int inf = 1000000007;
const ll INF = 1e18;
// int mod = 998244353;
int mod = 1000000007;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &s) {
  for (auto e : s)
    os << e;
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  (a += b % mod) %= mod;
  if (a < 0)
    a += mod;
}
template <class T> void operator+=(vector<T> &v, vector<T> v2) {
  rep(i, sz(v2)) v.eb(v2[i]);
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(12); // debuged
  int T;
  T = 1;
  while (T--)
    solve();
}

void solve() {
  int n, k;
  cin >> n >> k;
  vector<ll> a(n);
  cin >> a;

  vector<ll> b, c;
  rep(i, n) {
    if (a[i] > 0)
      b.eb(a[i]);
    else if (a[i] < 0)
      c.eb(-a[i]);
  }

  int flg = 0;
  ll ans;
  if (sz(b) + (sz(c) / 2 * 2) >= k)
    flg = 1;
  if (flg) {
    sort(all(b));
    sort(all(c));
    // cerr << b << endl << c << endl;
    ans = 1;
    if (k % 2) {
      ans = b.back();
      b.pop_back();
    }
    vector<ll> d;
    auto get = [&](vector<ll> b) {
      while (sz(b) >= 2) {
        ll tmp = b.back();
        b.pop_back();
        tmp *= b.back(); // mod 取らない !!
        b.pop_back();
        d.eb(tmp);
      }
    };
    get(b);
    get(c);
    sort(all(d));
    // cerr << d << endl;
    rep(i, k / 2) {
      (ans *= d.back() % mod) %= mod;
      d.pop_back();
    }
  } else {
    if (sz(b) + sz(c) != n) {
      ans = 0;
    } else {
      // とにかく絶対値小さいのを
      vector<pii> v(n);
      rep(i, n) v[i] = pii(abs(a[i]), a[i] > 0); // 0 はない
      sort(all(v));
      // rep(i, n) cerr << v[i] << endl;
      ans = 1;
      rep(i, k) {
        ll y = v[i].F;
        if (v[i].S == 0)
          (y = -y % mod + mod) %= mod;
        (ans *= y) %= mod;
      }
    }
  }
  cout << ans << endl;
}
/*
8 3
-366234132 -570811034 -825899702 -247819003 141930537 831482523 -241868851
959494248 ans : 547971197

4 3
-120078725 137721685 -839194760 -781735442
ans : 662908466

9 8
0 1 4 4 -10 -7 -2 9 9
ans : 0

15 12
9 -7 -6 -10 1 -2 -10 -9 8 -2 -10 -3 5 5 5
ans : 82399972

15 12
1 -7 -3 5 6 -3 -8 5 -6 8 9 6 5 3 -4
ans : 306367993
*/


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pli pair<ll, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define endl '\n'
const int inf = 1000000007;
const ll INF = 1e18;
// int mod = 998244353;
int mod = 1000000007;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <typename T, typename U> T pow_(T a, U b) {
  return b ? pow_(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
ll modpow(ll a, ll b, ll _mod) {
  return b ? modpow(a * a % _mod, b / 2, _mod) * (b % 2 ? a : 1) % _mod : 1;
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.F << " " << p.S;
  return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  rep(i, sz(vec)) {
    if (i)
      os << " ";
    os << vec[i];
  }
  return os;
}
template <class T> ostream &operator<<(ostream &os, const set<T> &s) {
  for (auto e : s)
    os << e;
  return os;
}
template <typename T> inline istream &operator>>(istream &is, vector<T> &v) {
  rep(j, sz(v)) is >> v[j];
  return is;
}
template <class T, class T2> inline void add(T &a, T2 b) {
  (a += b % mod) %= mod;
  if (a < 0)
    a += mod;
}
template <class T> void operator+=(vector<T> &v, vector<T> v2) {
  rep(i, sz(v2)) v.eb(v2[i]);
}

void solve();

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(12); // debuged
  int T;
  T = 1;
  while (T--)
    solve();
}

void solve() {
  int n, k;
  cin >> n >> k;
  vector<ll> a(n);
  cin >> a;

  vector<ll> b, c;
  rep(i, n) {
    if (a[i] > 0)
      b.eb(a[i]);
    else if (a[i] < 0)
      c.eb(-a[i]);
  }

  int flg = 0;
  ll ans;
  // 個数が足りてて, kが奇数なら正の数が1つ以上あるか
  if (sz(b) + (sz(c) / 2 * 2) >= k && (k % 2 == 0 || sz(b)))
    flg = 1;
  if (flg) {
    sort(all(b));
    sort(all(c));
    // cerr << b << endl << c << endl;
    ans = 1;
    if (k % 2) {
      ans = b.back();
      b.pop_back();
    }
    vector<ll> d;
    auto get = [&](vector<ll> b) {
      while (sz(b) >= 2) {
        ll tmp = b.back();
        b.pop_back();
        tmp *= b.back(); // mod 取らない !!
        b.pop_back();
        d.eb(tmp);
      }
    };
    get(b);
    get(c);
    sort(all(d));
    // cerr << d << endl;
    rep(i, k / 2) {
      (ans *= d.back() % mod) %= mod;
      d.pop_back();
    }
  } else {
    if (sz(b) + sz(c) != n) {
      ans = 0;
    } else {
      // とにかく絶対値小さいのを
      vector<pii> v(n);
      rep(i, n) v[i] = pii(abs(a[i]), a[i] > 0); // 0 はない
      sort(all(v));
      // rep(i, n) cerr << v[i] << endl;
      ans = 1;
      rep(i, k) {
        ll y = v[i].F;
        if (v[i].S == 0)
          (y = -y % mod + mod) %= mod;
        (ans *= y) %= mod;
      }
    }
  }
  cout << ans << endl;
}
/*
8 3
-366234132 -570811034 -825899702 -247819003 141930537 831482523 -241868851
959494248 ans : 547971197

4 3
-120078725 137721685 -839194760 -781735442
ans : 662908466

9 8
0 1 4 4 -10 -7 -2 9 9
ans : 0

15 12
9 -7 -6 -10 1 -2 -10 -9 8 -2 -10 -3 5 5 5
ans : 82399972

15 12
1 -7 -3 5 6 -3 -8 5 -6 8 9 6 5 3 -4
ans : 306367993
*/