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

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;

#define ff first
#define ss second
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define MX 200005
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \\
  int x;                                                                       \\
  cin >> x;                                                                    \\
  while (x--)
#define pw(b, p) pow(b, p) + 0.1
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

void codeforces() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}
int a[200005];
bool compare(int a, int b) {
  if (abs(a) > abs(b))
    return true;
  else
    return !true;
}
int modinv(int a, int n = mod - 2) {
  if (!n)
    return 1;
  int p = modinv(a, n / 2);
  p = (p * p) % mod;
  if (n & 1)
    return (p * a) % mod;
  return p;
}
int32_t main() {
  int n, k;
  cin >> n >> k;
  int flag = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] > 0)
      flag = 1;
  }
  if (k == n) {
    int ans = 1;
    for (int i = 0; i < k; i++) {
      ans = ans * (a[i] % mod);
      ans = (ans) % mod;
    }
    cout << (mod + ans) % mod;
    return 0;
  }
  if (flag == 0 and k % 2 == 1) {
    sort(a, a + n, greater<int>());
    int ans = 1;
    for (int i = 0; i < k; i++) {
      ans *= a[i];
      ans = (ans) % mod;
    }
    cout << (mod + ans) % mod << endl;
    return 0;
  }
  sort(a, a + n, compare);
  int ans = 1;
  int sign = 0;
  for (int i = 0; i < k; i++) {
    ans = ans * a[i];
    if (a[i] < 0)
      sign++;
    ans = (ans) % mod;
  }
  if (sign % 2 == 0)
    cout << (ans + mod) % mod;
  else {
    map<int, int> m;
    vector<int> s1, s2;
    for (int i = k; i < n; i++) {
      if (a[i] < 0)
        s1.pb(a[i]);
      else
        s2.pb(a[i]);
    }
    if (s1.size() > 0)
      sort(s1.begin(), s1.end());
    if (s2.size() > 0)
      sort(s2.begin(), s2.end());
    int x = 1, y = -1;
    if (s1.size() > 0)
      x = s1.front();
    if (s2.size() > 0)
      y = s2.back();
    s1.clear();
    s2.clear();
    for (int i = 0; i < k; i++) {
      m[a[i]]++;
      if (a[i] < 0)
        s1.pb(a[i]);
      else
        s2.pb(a[i]);
    }
    if (s1.size() > 0)
      sort(s1.begin(), s1.end());
    if (s2.size() > 0)
      sort(s2.begin(), s2.end());
    int t1 = 1, t2 = -1;
    if (s1.size() > 0)
      t1 = s1.back();
    if (s2.size() > 0)
      t2 = s2.front();
    if (x == 1 or t2 == -1) {
      m[t1]--;
      m[y]++;
    } else if (y == -1 or t1 == 1) {
      m[t2]--;
      m[x]++;
    } else if (x * t1 > y * t2) {
      m[t2]--;
      m[x]++;
    } else {
      m[t1]--;
      m[y]++;
    }
    ans = 1;
    for (auto &i : m) {
      for (int j = 0; j < i.ss; j++) {
        ans *= i.ff;
        ans = (ans) % mod;
      }
    }
    cout << ans << endl;
  }
  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;

#define ff first
#define ss second
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define MX 200005
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \\
  int x;                                                                       \\
  cin >> x;                                                                    \\
  while (x--)
#define pw(b, p) pow(b, p) + 0.1
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

void codeforces() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
}
int a[200005];
bool compare(int a, int b) {
  if (abs(a) > abs(b))
    return true;
  else
    return !true;
}
int modinv(int a, int n = mod - 2) {
  if (!n)
    return 1;
  int p = modinv(a, n / 2);
  p = (p * p) % mod;
  if (n & 1)
    return (p * a) % mod;
  return p;
}
int32_t main() {
  int n, k;
  cin >> n >> k;
  int flag = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] > 0)
      flag = 1;
  }
  if (k == n) {
    int ans = 1;
    for (int i = 0; i < k; i++) {
      ans = ans * (a[i] % mod);
      ans = (ans) % mod;
    }
    cout << (mod + ans) % mod;
    return 0;
  }
  if (flag == 0 and k % 2 == 1) {
    sort(a, a + n, greater<int>());
    int ans = 1;
    for (int i = 0; i < k; i++) {
      ans *= a[i];
      ans = (ans) % mod;
    }
    cout << (mod + ans) % mod << endl;
    return 0;
  }
  sort(a, a + n, compare);
  int ans = 1;
  int sign = 0;
  for (int i = 0; i < k; i++) {
    ans = ans * a[i];
    if (a[i] < 0)
      sign++;
    ans = (ans) % mod;
  }
  if (sign % 2 == 0)
    cout << (ans + mod) % mod;
  else {
    map<int, int> m;
    vector<int> s1, s2;
    for (int i = k; i < n; i++) {
      if (a[i] < 0)
        s1.pb(a[i]);
      else
        s2.pb(a[i]);
    }
    sort(s1.begin(), s1.end());
    sort(s2.begin(), s2.end());
    int x = s1.front();
    int y = s2.back();
    s1.clear();
    s2.clear();
    for (int i = 0; i < k; i++) {
      m[a[i]]++;
      if (a[i] < 0)
        s1.pb(a[i]);
      else
        s2.pb(a[i]);
    }
    sort(s1.begin(), s1.end());
    sort(s2.begin(), s2.end());
    int t1 = s1.back();
    int t2 = s2.front();
    if (x * t1 > y * t2) {
      m[t2]--;
      m[x]++;
    } else {
      m[t1]--;
      m[y]++;
    }
    ans = 1;
    for (auto &i : m) {
      for (int j = 0; j < i.ss; j++) {
        ans *= i.ff;
        ans = (ans) % mod;
      }
    }
    cout << ans << endl;
  }
  return 0;
}