Problem p03651 (C++)

Buggy submission (status: Runtime Error):
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <random>
#include <unordered_map>
#include <unordered_set>

using namespace std;

// 呪文
#define DUMPOUT cerr
#define dump(...)                                                              \
  DUMPOUT << "  ";                                                             \
  DUMPOUT << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef pair<string, string> pss;
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const pair<_KTy, _Ty> &m) {
  ostr << "{" << m.first << ", " << m.second << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const map<_KTy, _Ty> &m) {
  if (m.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *m.begin();
  for (auto itr = ++m.begin(); itr != m.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const unordered_map<_KTy, _Ty> &m) {
  if (m.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *m.begin();
  for (auto itr = ++m.begin(); itr != m.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty>
ostream &operator<<(ostream &ostr, const vector<_Ty> &v) {
  if (v.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << v.front();
  for (auto itr = ++v.begin(); itr != v.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty> ostream &operator<<(ostream &ostr, const set<_Ty> &s) {
  if (s.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *(s.begin());
  for (auto itr = ++s.begin(); itr != s.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty>
ostream &operator<<(ostream &ostr, const stack<_Ty> &s) {
  if (s.empty()) {
    ostr << "{ }";
    return ostr;
  }
  stack<_Ty> t(s);
  ostr << "{" << t.top();
  t.pop();
  while (!t.empty()) {
    ostr << ", " << t.top();
    t.pop();
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty> ostream &operator<<(ostream &ostr, const list<_Ty> &l) {
  if (l.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << l.front();
  for (auto itr = ++l.begin(); itr != l.end(); ++itr) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
istream &operator>>(istream &istr, pair<_KTy, _Ty> &m) {
  istr >> m.first >> m.second;
  return istr;
}
template <typename _Ty> istream &operator>>(istream &istr, vector<_Ty> &v) {
  for (size_t i = 0; i < v.size(); i++)
    istr >> v[i];
  return istr;
}
namespace aux { // print tuple
template <typename Ty, unsigned N, unsigned L> struct tp {
  static void print(ostream &os, const Ty &v) {
    os << get<N>(v) << ", ";
    tp<Ty, N + 1, L>::print(os, v);
  }
};
template <typename Ty, unsigned N> struct tp<Ty, N, N> {
  static void print(ostream &os, const Ty &value) { os << get<N>(value); }
};
} // namespace aux
template <typename... Tys>
ostream &operator<<(ostream &os, const tuple<Tys...> &t) {
  os << "{";
  aux::tp<tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t);
  os << "}";
  return os;
}

template <typename A, size_t N, typename T>
inline void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0) {
    DUMPOUT << " ";
  } else {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}

#define PI 3.14159265358979323846
#define EPS 1e-8
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define fake false

template <typename Ty> Ty GCD(Ty m, Ty n) {
  Ty k;
  do {
    k = m % n;
    m = n;
    n = k;
  } while (k != 0);
  return m;
}

int main() {

  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  ll K;
  cin >> N >> K;
  vector<ll> A(N);
  cin >> A;

  sort(all(A));

  bool flag = false;
  for (int i = 0; i < N; i++) {
    if (A[i] >= K)
      flag = true;
  }
  if (!flag) {
    cout << "IMPOSSIBLE" << endl;
    return 0;
  }

  ll g = A[0];
  for (int i = 0; i < N - 1; i++) {
    g = GCD(g, abs(A[i + 1] - A[i]));
  }

  if (K % g == 0)
    cout << "POSSIBLE" << endl;
  else
    cout << "IMPOSSIBLE" << endl;

  return 0;
}

Fixed submission:
#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <random>
#include <unordered_map>
#include <unordered_set>

using namespace std;

// 呪文
#define DUMPOUT cerr
#define dump(...)                                                              \
  DUMPOUT << "  ";                                                             \
  DUMPOUT << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef pair<string, string> pss;
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const pair<_KTy, _Ty> &m) {
  ostr << "{" << m.first << ", " << m.second << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const map<_KTy, _Ty> &m) {
  if (m.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *m.begin();
  for (auto itr = ++m.begin(); itr != m.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
ostream &operator<<(ostream &ostr, const unordered_map<_KTy, _Ty> &m) {
  if (m.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *m.begin();
  for (auto itr = ++m.begin(); itr != m.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty>
ostream &operator<<(ostream &ostr, const vector<_Ty> &v) {
  if (v.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << v.front();
  for (auto itr = ++v.begin(); itr != v.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty> ostream &operator<<(ostream &ostr, const set<_Ty> &s) {
  if (s.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << *(s.begin());
  for (auto itr = ++s.begin(); itr != s.end(); itr++) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty>
ostream &operator<<(ostream &ostr, const stack<_Ty> &s) {
  if (s.empty()) {
    ostr << "{ }";
    return ostr;
  }
  stack<_Ty> t(s);
  ostr << "{" << t.top();
  t.pop();
  while (!t.empty()) {
    ostr << ", " << t.top();
    t.pop();
  }
  ostr << "}";
  return ostr;
}
template <typename _Ty> ostream &operator<<(ostream &ostr, const list<_Ty> &l) {
  if (l.empty()) {
    ostr << "{ }";
    return ostr;
  }
  ostr << "{" << l.front();
  for (auto itr = ++l.begin(); itr != l.end(); ++itr) {
    ostr << ", " << *itr;
  }
  ostr << "}";
  return ostr;
}
template <typename _KTy, typename _Ty>
istream &operator>>(istream &istr, pair<_KTy, _Ty> &m) {
  istr >> m.first >> m.second;
  return istr;
}
template <typename _Ty> istream &operator>>(istream &istr, vector<_Ty> &v) {
  for (size_t i = 0; i < v.size(); i++)
    istr >> v[i];
  return istr;
}
namespace aux { // print tuple
template <typename Ty, unsigned N, unsigned L> struct tp {
  static void print(ostream &os, const Ty &v) {
    os << get<N>(v) << ", ";
    tp<Ty, N + 1, L>::print(os, v);
  }
};
template <typename Ty, unsigned N> struct tp<Ty, N, N> {
  static void print(ostream &os, const Ty &value) { os << get<N>(value); }
};
} // namespace aux
template <typename... Tys>
ostream &operator<<(ostream &os, const tuple<Tys...> &t) {
  os << "{";
  aux::tp<tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t);
  os << "}";
  return os;
}

template <typename A, size_t N, typename T>
inline void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0) {
    DUMPOUT << " ";
  } else {
    DUMPOUT << ", ";
  }
  dump_func(std::move(tail)...);
}

#define PI 3.14159265358979323846
#define EPS 1e-8
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define fake false

template <typename Ty> Ty GCD(Ty m, Ty n) {
  Ty k;
  do {
    k = m % n;
    m = n;
    n = k;
  } while (k != 0);
  return m;
}

int main() {

  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  ll K;
  cin >> N >> K;
  vector<ll> A(N);
  cin >> A;

  sort(all(A));

  bool flag = false;
  for (int i = 0; i < N; i++) {
    if (A[i] >= K)
      flag = true;
  }
  if (!flag) {
    cout << "IMPOSSIBLE" << endl;
    return 0;
  }

  ll g = A[0];
  for (int i = 0; i < N - 1; i++) {
    if (A[i + 1] == A[i])
      continue;
    g = GCD(g, abs(A[i + 1] - A[i]));
  }

  if (K % g == 0)
    cout << "POSSIBLE" << endl;
  else
    cout << "IMPOSSIBLE" << endl;

  return 0;
}