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

#include <bits/stdc++.h>
#define int long long
using namespace std;

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

const int MOD = 1e9 + 7;

signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  sort(a.begin(), a.end(), cmp);
  int afterpos = -1337, afterneg = 1337, insidepos = -1337, insideneg = 1337;
  int cntneg = 0, cntpos = 0;
  for (int i = 0; i < k; i++) {
    if (a[i] < 0)
      insideneg = a[i], cntneg++;
    else
      insidepos = a[i], cntpos++;
  }
  for (int i = n - 1; i >= k; i--) {
    if (a[i] < 0)
      afterneg = a[i];
    else
      afterpos = a[i];
  }

  int prod = 1;
  if (cntneg % 2 == 0) {
    for (int i = 0; i < k; i++)
      prod *= abs(a[i]), prod %= MOD;
    cout << prod;
    return 0;
  } else {
    int f = 0;
    if ((afterpos == -1337 && insidepos == -1337) ||
        n == k) { /// If all are negative
      for (int i = n - k; i < n; i++)
        prod *= a[i] + MOD, prod %= MOD;
      cout << prod;
      return 0;
    } else if ((afterpos == -1337 || insideneg == 1337) && afterneg != 1337 &&
               insidepos != -1337) { /// If only pos -> neg
      for (int i = 0; i < k; i++) {
        if (!f && a[i] == insidepos)
          f = 1, prod *= abs(afterneg), prod %= MOD;
        else
          prod *= abs(a[i]), prod %= MOD;
      }
      cout << prod;
      return 0;
    } else if ((afterneg == 1337 || insidepos == -1337) && insideneg != 1337 &&
               afterpos != -1337) { /// If only neg -> pos
      for (int i = 0; i < k; i++) {
        if (!f && a[i] == insideneg)
          f = 1, prod *= abs(afterpos), prod %= MOD;
        else
          prod *= abs(a[i]), prod %= MOD;
      }
      cout << prod;
      return 0;
    } else if (afterneg != 1337 && insidepos != -1337 && insideneg != 1337 &&
               afterpos != -1337) { /// If both possible
      int a1 = abs(insidepos * afterpos);
      int a2 = abs(insideneg * afterneg);
      if (a1 > a2) {
        for (int i = 0; i < k; i++) {
          if (!f && a[i] == insideneg)
            f = 1, prod *= abs(afterpos), prod %= MOD;
          else
            prod *= abs(a[i]), prod %= MOD;
        }
        cout << prod;
        return 0;
      } else {
        for (int i = 0; i < k; i++) {
          if (!f && a[i] == insidepos)
            f = 1, prod *= abs(afterneg), prod %= MOD;
          else
            prod *= abs(a[i]), prod %= MOD;
        }
        cout << prod;
        return 0;
      }
    }
  }
  assert(false);
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>
#define int long long
using namespace std;

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

const int MOD = 1e9 + 7;

signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  sort(a.begin(), a.end(), cmp);
  int afterpos = -1337, afterneg = 1337, insidepos = -1337, insideneg = 1337;
  int cntneg = 0, cntpos = 0;
  for (int i = 0; i < k; i++) {
    if (a[i] < 0)
      insideneg = a[i], cntneg++;
    else
      insidepos = a[i], cntpos++;
  }
  for (int i = n - 1; i >= k; i--) {
    if (a[i] < 0)
      afterneg = a[i];
    else
      afterpos = a[i];
  }
  int prod = 1;
  if (cntneg % 2 == 0) {
    for (int i = 0; i < k; i++)
      prod *= abs(a[i]), prod %= MOD;
    cout << prod;
    return 0;
  } else {
    int f = 0;
    if ((afterpos == -1337 && insidepos == -1337) ||
        n == k) { /// If all are negative
      for (int i = n - k; i < n; i++)
        prod *= a[i] + MOD, prod %= MOD;
      cout << prod;
      return 0;
    } else if (afterpos == -1337 && afterneg != 1337 &&
               insidepos != -1337) { /// If only pos -> neg
      for (int i = 0; i < k; i++) {
        if (!f && a[i] == insidepos)
          f = 1, prod *= abs(afterneg), prod %= MOD;
        else
          prod *= abs(a[i]), prod %= MOD;
      }
      cout << prod;
      return 0;
    } else if (afterneg == 1337 && insideneg != 1337 &&
               afterpos != -1337) { /// If only neg -> pos
      for (int i = 0; i < k; i++) {
        if (!f && a[i] == insideneg)
          f = 1, prod *= abs(afterpos), prod %= MOD;
        else
          prod *= abs(a[i]), prod %= MOD;
      }
      cout << prod;
      return 0;
    } else if (afterneg != 1337 && insidepos != -1337 && insideneg != 1337 &&
               afterpos != -1337) { /// If both possible
      int a1 = abs(insidepos * afterpos);
      int a2 = abs(insideneg * afterneg);
      if (a1 > a2) {
        for (int i = 0; i < k; i++) {
          if (!f && a[i] == insideneg)
            f = 1, prod *= abs(afterpos), prod %= MOD;
          else
            prod *= abs(a[i]), prod %= MOD;
        }
        cout << prod;
        return 0;
      } else {
        for (int i = 0; i < k; i++) {
          if (!f && a[i] == insidepos)
            f = 1, prod *= abs(afterneg), prod %= MOD;
          else
            prod *= abs(a[i]), prod %= MOD;
        }
        cout << prod;
        return 0;
      }
    }
  }
  assert(false);
}