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

#include <bits/stdc++.h>
using namespace std;
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
//
//     #pragma GCC optimize("unroll-loops")
//     #pragma GCC optimize("Ofast")
//     #pragma GCC optimize("-O3")
//     #pragma GCC optimize("no-stack-protector")
//     #pragma GCC optimize("fast-math")
// #define LOCAL
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cout << *x, 0);
sim > char dud(...);
struct debug {
#ifndef LOCAL
  ~debug() { cout << endl; }
  eni(!=) cout << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define fi first
#define f first
#define se second
#define s second
#define vi_a vector<int> a;
#define p_b push_back
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ll long long
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ld long double
#define pll pair<ll, ll>
#define pii pair<int, int>
#define m_p make_pair
#define fast_io                                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);                                                                 \\
  ios_base::sync_with_stdio(0);
#define all(x) x.begin(), x.end()
#define getfiles                                                               \\
  ifstream cin("input.txt");                                                   \\
  ofstream cout("output.txt");
#define pw(x) (1ll << x)
#define sz(x) (ll) x.size()

#define rall(x) x.rbegin(), x.rend()
#define len(a) (ll) a.size()
#define rep(x, l, r) for (ll x = l; x < r; x++)

// using namespace __gnu_pbds;
ld eps = (ld)1 / 1e6;
const ld pi = 3.14159265359;
ll inf = 1e18, mod1 = 1e9 + 7;
ll sqr(ll a) { return a * a; }
ll qb(ll a) { return a * a * a; }
ll gcd(ll a, ll b) { return !a ? b : gcd(b % a, a); }
ll binpow(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod
                    : sqr(binpow(a, b / 2, mod)) % mod)
           : 1;
}
ll binmult(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod
                    : (2 * binmult(a, b / 2, mod)) % mod)
           : 0;
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
const ll R = 1e4;
const ll tx[4] = {0, 0, -1, 1};
const ll ty[4] = {-1, 1, 0, 0};
const char rev_to[4] = {'E', 'W', 'N', 'S'};
const int N = 1e6 + 1;
const int M = 1e9 + 7;
signed main() {
  fast_io;
  int n, k;
  cin >> n >> k;
  vector<ll> a(n);
  vector<ll> b, c;
  int x;
  for (int i = 0; i < n; i++) {
    cin >> x;
    if (x < 0) {
      b.p_b(x);
    } else {
      c.p_b(x);
    }
  }
  sort(rall(b));
  sort(all(c));
  int f = sz(c) - 1, s = sz(b) - 1;
  ll ans = 1;
  vector<ll> who;
  if (k % 2) {
    if (!sz(c)) {
      for (int i = 0; i < k; i++) {
        ans = (ans * b[i]) % mod1;
      }
      if (ans < 0)
        ans += mod1;
      cout << ans;
      return 0;
    } else {
      k--;
      f--;
      who.p_b(c.back());
    }
  }
  while (k > 0 && f >= 1 && s >= 1) {
    if (b[s] * b[s - 1] > c[f] * c[f - 1]) {
      who.p_b(b[s]);
      who.p_b(b[s - 1]);
      k -= 2;
      s -= 2;
    } else {
      who.p_b(c[f]);
      who.p_b(c[f - 1]);
      k -= 2;
      f -= 2;
    }
  }
  while (k > 0 && s >= 1) {
    who.p_b(b[s]);
    who.p_b(b[s - 1]);
    k -= 2;
    s -= 2;
  }
  while (k > 0 && f >= 1) {
    who.p_b(c[f]);
    who.p_b(c[f - 1]);
    k -= 2;
    f -= 2;
  }
  while (k > 0) {
    if (s)
      who.p_b(c[f]), f--;
    else
      who.p_b(b[s]), s--;
    k--;
  }
  for (auto &z : who) {
    ans = (ans * z) % mod1;
  }
  if (ans == -1) {
    if (sz(c) && c[0] == 0)
      ans = 0;
  }
  if (ans < 0)
    ans += mod1;
  cout << ans;
  return 0;
}
/// stuff you should look for :
/*


        * int overflow, array bounds
        * special cases (n=1?)
        * do smth instead of nothing and stay organized
        * read the conditions carefully
        * WRITE STUFF DOWN
*/


Error: WA

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
//
//     #pragma GCC optimize("unroll-loops")
//     #pragma GCC optimize("Ofast")
//     #pragma GCC optimize("-O3")
//     #pragma GCC optimize("no-stack-protector")
//     #pragma GCC optimize("fast-math")
// #define LOCAL
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cout << *x, 0);
sim > char dud(...);
struct debug {
#ifndef LOCAL
  ~debug() { cout << endl; }
  eni(!=) cout << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define fi first
#define f first
#define se second
#define s second
#define vi_a vector<int> a;
#define p_b push_back
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ll long long
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ld long double
#define pll pair<ll, ll>
#define pii pair<int, int>
#define m_p make_pair
#define fast_io                                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);                                                                 \\
  ios_base::sync_with_stdio(0);
#define all(x) x.begin(), x.end()
#define getfiles                                                               \\
  ifstream cin("input.txt");                                                   \\
  ofstream cout("output.txt");
#define pw(x) (1ll << x)
#define sz(x) (ll) x.size()

#define rall(x) x.rbegin(), x.rend()
#define len(a) (ll) a.size()
#define rep(x, l, r) for (ll x = l; x < r; x++)

// using namespace __gnu_pbds;
ld eps = (ld)1 / 1e6;
const ld pi = 3.14159265359;
ll inf = 1e18, mod1 = 1e9 + 7;
ll sqr(ll a) { return a * a; }
ll qb(ll a) { return a * a * a; }
ll gcd(ll a, ll b) { return !a ? b : gcd(b % a, a); }
ll binpow(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod
                    : sqr(binpow(a, b / 2, mod)) % mod)
           : 1;
}
ll binmult(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod
                    : (2 * binmult(a, b / 2, mod)) % mod)
           : 0;
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
const ll R = 1e4;
const ll tx[4] = {0, 0, -1, 1};
const ll ty[4] = {-1, 1, 0, 0};
const char rev_to[4] = {'E', 'W', 'N', 'S'};
const int N = 1e6 + 1;
const int M = 1e9 + 7;
signed main() {
  fast_io;
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  vector<int> b, c;
  int x;
  for (int i = 0; i < n; i++) {
    cin >> x;
    if (x < 0) {
      b.p_b(x);
    } else {
      c.p_b(x);
    }
  }
  sort(rall(b));
  sort(all(c));
  int f = sz(c) - 1, s = sz(b) - 1;
  ll ans = 1;
  vector<ll> who;
  if (k % 2) {
    if (!sz(c)) {
      for (int i = 0; i < k; i++) {
        ans = (ans * b[i]) % mod1;
      }
      if (ans < 0)
        ans += mod1;
      cout << ans;
      return 0;
    } else {
      k--;
      f--;
      who.p_b(c.back());
    }
  }
  while (f >= 1 && s >= 1) {
    if (b[s] * b[s - 1] > c[f] * c[f - 1]) {
      who.p_b(b[s]);
      who.p_b(b[s - 1]);
      k -= 2;
      s -= 2;
    } else {
      who.p_b(c[f]);
      who.p_b(c[f - 1]);
      k -= 2;
      f -= 2;
    }
  }
  while (k) {
    if (s)
      who.p_b(c[f]), f--;
    else
      who.p_b(b[s]), s--;
    k--;
  }
  for (auto &z : who) {
    ans = (ans * z) % mod1;
  }
  if (ans < 0)
    ans += mod1;
  cout << ans;
  return 0;
}
/// stuff you should look for :
/*


        * int overflow, array bounds
        * special cases (n=1?)
        * do smth instead of nothing and stay organized
        * read the conditions carefully
        * WRITE STUFF DOWN
*/