Problem p02616 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#include <math.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define PI 3.14159265359
using namespace std;
using ll = long long;
using P = pair<int, int>;

const int mod = 1000000007;
struct mint {
  ll x;
  mint(ll x = 0) : x(x % 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 {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};

bool comp(int a, int b) { return abs(a) > abs(b); }

int main() {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  int mall = 0;
  rep(i, n) {
    cin >> a[i];
    if (a[i] < 0)
      mall++;
  }

  mint ans = 1;
  if (mall == n && k % 2 == 1) {
    sort(a.begin(), a.end());
    reverse(a.begin(), a.end());
    rep(i, k) ans *= (a[i] + 1000000007);
    cout << ans.x << endl;
    return 0;
  }

  sort(a.begin(), a.end(), comp);

  int m = 0;
  rep(i, k) {
    ans *= (a[i] + 1000000007);
    if (a[i] < 0)
      m++;
  }

  bool flug = true;
  for (int i = k; i < n; i++) {
    if (a[i] > 0)
      flug = false;
  }

  if (m % 2 == 0 || n == k || ans.x == 0 || (m % 2 == 0 && flug)) {
    cout << ans.x << endl;
  } else {
    ll pmin = -1, mmax = 1, mmin = 1, pmax = -1;
    for (int i = k - 1; i >= 0; i--) {
      if (a[i] >= 0 && pmin == -1) {
        pmin = a[i];
      }
      if (a[i] < 0 && mmin == 1) {
        mmin = a[i];
      }
    }
    for (int i = k; i < n; i++) {
      if (a[i] < 0 && mmax == 1) {
        mmax = a[i];
      }
      if (a[i] >= 0 && pmax == -1) {
        pmax = a[i];
      }
    }
    ll mm = mmax * mmin, pp = pmax * pmin;
    if (pmax == -1 || mmin == 1) {
      ans = ans / pmin * (mmax + 1000000007);
    } else if (mmax == 1 || pmin == -1) {
      ans = ans / (mmin + 1000000007) * pmax;
    } else if (mm > pp) {
      ans = ans / pmin * (mmax + 1000000007);
    } else {
      ans = ans / (mmin + 1000000007) * pmax;
    }
    cout << ans.x << endl;
  }

  return 0;
}
/*
 */


Error: 0

Fixed submission:

#include <bits/stdc++.h>
#include <math.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define PI 3.14159265359
using namespace std;
using ll = long long;
using P = pair<int, int>;

const int mod = 1000000007;
struct mint {
  ll x;
  mint(ll x = 0) : x(x % 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 {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};

bool comp(int a, int b) { return abs(a) > abs(b); }

int main() {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  int mall = 0;
  rep(i, n) {
    cin >> a[i];
    if (a[i] < 0)
      mall++;
  }

  mint ans = 1;
  if (mall == n && k % 2 == 1) {
    sort(a.begin(), a.end());
    reverse(a.begin(), a.end());
    rep(i, k) ans *= (a[i] + 1000000007);
    cout << ans.x << endl;
    return 0;
  }

  sort(a.begin(), a.end(), comp);

  int m = 0;
  rep(i, k) {
    ans *= (a[i] + 1000000007);
    if (a[i] < 0)
      m++;
  }

  bool flug = true;
  for (int i = k; i < n; i++) {
    if (a[i] > 0)
      flug = false;
  }

  if (m % 2 == 0 || n == k || ans.x == 0 || (m % 2 == 0 && flug)) {
    cout << ans.x << endl;
  } else {
    ll pmin = 0, mmax = 0, mmin = 0, pmax = 0;
    for (int i = k - 1; i >= 0; i--) {
      if (a[i] > 0 && pmin == 0) {
        pmin = a[i];
      }
      if (a[i] < 0 && mmin == 0) {
        mmin = a[i];
      }
    }
    for (int i = k; i < n; i++) {
      if (a[i] < 0 && mmax == 0) {
        mmax = a[i];
      }
      if (a[i] > 0 && pmax == 0) {
        pmax = a[i];
      }
    }
    ll mm = mmax * mmin, pp = pmax * pmin;
    if (mm > pp) {
      ans = ans.x / pmin * mmax;
    } else {
      ans = ans.x / mmin * pmax;
    }
    cout << ans.x << endl;
  }

  return 0;
}
/*
 */