Problem p02616 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#ifdef LOCAL_DEBUG
#define DEBUG 1
#define CERR                                                                   \
  if (DEBUG)                                                                   \
  cerr
#define MACRO(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, NAME, ...) NAME
#define pr(...)                                                                \
  CERR << MACRO(__VA_ARGS__, pr10, pr9, pr8, pr7, pr6, pr5, pr4, pr3, pr2,     \
                pr1)(__VA_ARGS__)                                              \
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define pr9(a, b, c, d, e, f, g, h, i) pr1(a) << pr8(b, c, d, e, f, g, h, i)
#define pr10(a, b, c, d, e, f, g, h, i, j)                                     \
  pr1(a) << pr9(b, c, d, e, f, g, h, i, j)
#define prArr(a)                                                               \
  {                                                                            \
    CERR << (#a) << "={";                                                      \
    int i = 0;                                                                 \
    for (auto t : (a))                                                         \
      CERR << (i++ ? ", " : "") << t;                                          \
    CERR << "}" << endl;                                                       \
  }
#else
#define DEBUG 0
#define pr(...)
#define prArr(a)
#endif
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL << 60) + 1e9; // ~ 1.15 * 1e18
const Int mod = (1e9) + 7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE

Int mod_pow(Int x, Int y) {
  Int res = 1;
  while (y) {
    if (y & 1)
      res = res * x % mod;
    x = x * x % mod;
    y /= 2;
  }
  return res;
}

signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  Int N, K;
  cin >> N >> K;
  vector<Int> A(N);
  cin >> A;
  sort(A.begin(), A.end(), [&](Int a, Int b) { return abs(a) > abs(b); });

  Int base = 1;
  { // すべてかけたら+
    Int cnt = 0;
    for (Int i = 0; i < K; i++) {
      if (A[i] < 0)
        cnt++;
      if (A[i] == 0) {
        cout << 0 << endl;
        return 0;
      }
      base = base * abs(A[i]);
      base %= mod;
    }
    if (cnt % 2 == 0) {
      cout << base << endl;
      return 0;
    }
  }

  Int a = 1, b = -1; // 負-1、正+1
  Int x = -1, y = 1; // 正-1、負+1
  for (Int i = 0; i < K; i++) {
    if (A[i] < 0)
      a = A[i];
    if (A[i] > 0)
      x = A[i];
  }

  for (Int i = K; i < N; i++) {
    if (A[i] > 0 && b == -1)
      b = A[i];
    if (A[i] < 0 && y == 1)
      y = A[i];
  }

  if ((a == 1 || b == -1) && (x == -1 || y == 1)) {
    Int ans = 1;
    Int cnt = 0;
    for (Int i = 0; i < K; i++) {
      ans = ans * abs(A[N - 1 - i]) % mod;
      if (A[N - 1 - i] < 0)
        cnt++;
    }
    assert(cnt % 2 == 1);
    cout << (mod - ans) % mod << endl;
    return 0;
  }

  if (a == 1 || b == -1) {
    Int ans = base * mod_pow(abs(x), mod - 2) % mod;
    ans = ans * abs(y) % mod;
    cout << ans << endl;
    return 0;
  }

  if (x == -1 || y == 1) {
    Int ans = base * mod_pow(abs(a), mod - 2) % mod;
    ans = ans * abs(b) % mod;
    cout << ans << endl;
    return 0;
  }

  // if(b / a < y / x)
  if (b * x < y * a) {
    Int ans = base * mod_pow(abs(x), mod - 2) % mod;
    ans = ans * abs(y) % mod;
    cout << ans << endl;
    return 0;
  }

  Int ans = base * mod_pow(abs(a), mod - 2) % mod;
  ans = ans * abs(b) % mod;
  cout << ans << endl;
  return 0;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#ifdef LOCAL_DEBUG
#define DEBUG 1
#define CERR                                                                   \
  if (DEBUG)                                                                   \
  cerr
#define MACRO(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, NAME, ...) NAME
#define pr(...)                                                                \
  CERR << MACRO(__VA_ARGS__, pr10, pr9, pr8, pr7, pr6, pr5, pr4, pr3, pr2,     \
                pr1)(__VA_ARGS__)                                              \
       << endl
#define pr1(a) (#a) << "=" << (a) << " "
#define pr2(a, b) pr1(a) << pr1(b)
#define pr3(a, b, c) pr1(a) << pr2(b, c)
#define pr4(a, b, c, d) pr1(a) << pr3(b, c, d)
#define pr5(a, b, c, d, e) pr1(a) << pr4(b, c, d, e)
#define pr6(a, b, c, d, e, f) pr1(a) << pr5(b, c, d, e, f)
#define pr7(a, b, c, d, e, f, g) pr1(a) << pr6(b, c, d, e, f, g)
#define pr8(a, b, c, d, e, f, g, h) pr1(a) << pr7(b, c, d, e, f, g, h)
#define pr9(a, b, c, d, e, f, g, h, i) pr1(a) << pr8(b, c, d, e, f, g, h, i)
#define pr10(a, b, c, d, e, f, g, h, i, j)                                     \
  pr1(a) << pr9(b, c, d, e, f, g, h, i, j)
#define prArr(a)                                                               \
  {                                                                            \
    CERR << (#a) << "={";                                                      \
    int i = 0;                                                                 \
    for (auto t : (a))                                                         \
      CERR << (i++ ? ", " : "") << t;                                          \
    CERR << "}" << endl;                                                       \
  }
#else
#define DEBUG 0
#define pr(...)
#define prArr(a)
#endif
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL << 60) + 1e9; // ~ 1.15 * 1e18
const Int mod = (1e9) + 7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int, Int>;
template <class T> T Max(T &a, T b) { return a = max(a, b); }
template <class T> T Min(T &a, T b) { return a = min(a, b); }
template <class T1, class T2> ostream &operator<<(ostream &o, pair<T1, T2> p) {
  return o << "(" << p.first << "," << p.second << ")";
}
template <class T1, class T2, class T3>
ostream &operator<<(ostream &o, tuple<T1, T2, T3> t) {
  return o << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class T1, class T2> istream &operator>>(istream &i, pair<T1, T2> &p) {
  return i >> p.first >> p.second;
}
template <class T> ostream &operator<<(ostream &o, vector<T> a) {
  Int i = 0;
  for (T t : a)
    o << (i++ ? " " : "") << t;
  return o;
}
template <class T> istream &operator>>(istream &i, vector<T> &a) {
  for (T &t : a)
    i >> t;
  return i;
}
// INSERT ABOVE HERE

Int mod_pow(Int x, Int y) {
  Int res = 1;
  while (y) {
    if (y & 1)
      res = res * x % mod;
    x = x * x % mod;
    y /= 2;
  }
  return res;
}

signed main() {
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  Int N, K;
  cin >> N >> K;
  vector<Int> A(N);
  cin >> A;
  sort(A.begin(), A.end(), [&](Int a, Int b) { return abs(a) > abs(b); });

  Int base = 1;
  { // すべてかけたら+
    Int cnt = 0;
    for (Int i = 0; i < K; i++) {
      if (A[i] < 0)
        cnt++;
      if (A[i] == 0) {
        cout << 0 << endl;
        return 0;
      }
      base = base * abs(A[i]);
      base %= mod;
    }
    if (cnt % 2 == 0) {
      cout << base << endl;
      return 0;
    }
  }

  Int a = 1, b = -1; // 負-1、正+1
  Int x = -1, y = 1; // 正-1、負+1
  for (Int i = 0; i < K; i++) {
    if (A[i] < 0)
      a = A[i];
    if (A[i] > 0)
      x = A[i];
  }

  for (Int i = K; i < N; i++) {
    if (A[i] > 0 && b == -1)
      b = A[i];
    if (A[i] < 0 && y == 1)
      y = A[i];
  }

  if ((a == 1 || b == -1) && (x == -1 || y == 1)) {
    Int ans = 1;
    Int cnt = 0;
    for (Int i = 0; i < K; i++) {
      ans = ans * abs(A[N - 1 - i]) % mod;
      if (A[N - 1 - i] < 0)
        cnt++;
    }
    // assert(cnt%2 == 1);
    if (cnt % 2 == 0) {
      cout << ans << endl;
      return 0;
    }
    cout << (mod - ans) % mod << endl;
    return 0;
  }

  if (a == 1 || b == -1) {
    Int ans = base * mod_pow(abs(x), mod - 2) % mod;
    ans = ans * abs(y) % mod;
    cout << ans << endl;
    return 0;
  }

  if (x == -1 || y == 1) {
    Int ans = base * mod_pow(abs(a), mod - 2) % mod;
    ans = ans * abs(b) % mod;
    cout << ans << endl;
    return 0;
  }

  // if(b / a < y / x)
  if (b * x < y * a) {
    Int ans = base * mod_pow(abs(x), mod - 2) % mod;
    ans = ans * abs(y) % mod;
    cout << ans << endl;
    return 0;
  }

  Int ans = base * mod_pow(abs(a), mod - 2) % mod;
  ans = ans * abs(b) % mod;
  cout << ans << endl;
  return 0;

  return 0;
}