Problem p03651 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

/* template {{{ */
/* vim: set foldmethod=marker: */
/* Roadagain {{{ */
/****************************************************************************************/
/*                                                                                      */
/*                                                                                      */
/*                                                                                      */
/*  /#######                            /##                               /## */
/* | ##__  ##                          | ##                              |__/ */
/* | ##  \ ##  /######   /######   /#######  /######   /######   /######  /##
 * /#######  */
/* | #######/ /##__  ## |____  ## /##__  ## |____  ## /##__  ## |____  ##| ##|
 * ##__  ## */
/* | ##__  ##| ##  \ ##  /#######| ##  | ##  /#######| ##  \ ##  /#######| ##|
 * ##  \ ## */
/* | ##  \ ##| ##  | ## /##__  ##| ##  | ## /##__  ##| ##  | ## /##__  ##| ##|
 * ##  | ## */
/* | ##  | ##|  ######/|  #######|  #######|  #######|  #######|  #######| ##|
 * ##  | ## */
/* |__/  |__/ \______/  \_______/ \_______/ \_______/ \____  ##
 * \_______/|__/|__/  |__/ */
/*                                                    /##  \ ## */
/*                                                   |  ######/ */
/*                                                    \______/ */
/*                                                                                      */
/****************************************************************************************/
/* }}} */
/* constant {{{ */
const int INF = (int)1e9;
const int MOD = (int)1e9 + 7;
const double PI = acos(-1);
const double EPS = 1e-14;
/* }}} */
/* alias {{{ */
template <class T> using vec = vector<T>;
using ll = long long;
using ull = unsigned long long;
using vi = vec<int>;
using vl = vec<ll>;
using vd = vec<double>;
using pii = pair<int, int>;
using pdd = pair<double, double>;
using vec2 = complex<double>;
/* }}} */
/* repetition {{{ */
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define RFOR(i, a, b) for (int i = (int)(b)-1; i >= (int)(a); --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define REPIT(i, obj) for (auto i = (obj).begin(); i != (obj).end(); ++i)
#define RREPIT(i, obj) for (auto i = (obj).rbegin(); i != (obj).rend(); ++i)
/* }}} */
/* short {{{ */
#define pb emplace_back
#define mp make_pair
#define fst first
#define sec second
/* }}} */
/* input {{{ */
template <class T = int> inline T in() {
  T x;
  cin >> x;
  return x;
}
template <class T = int> inline vec<T> in(int n) {
  vec<T> v(n);
  REP(i, n) v[i] = in<T>();
  return v;
}
template <class T = int> inline void in(T *x, int n) {
  REP(i, n) x[i] = in<T>();
}
#define inl in<ll>
#define ind in<double>
#define ins in<string>
/* }}} */
/* container util {{{ */
#define ALL(obj) (obj).begin(), (obj).end()
#define ALLA(ary, n) (ary), ((ary) + (n))
#define RALL(obj) (obj).rbegin(), (obj).rend()
#define SZ(obj) (obj).size()
#define SZA(ary) (sizeof(ary) / sizeof(*ary))
#define SORT(obj) sort(ALL(obj))
#define SORTA(ary, n) sort(ALLA(ary, n))
#define EXIST(obj, key) ((obj).find(key) != (obj).end())
#define CLEARY(ary) memset((ary), 0, sizeof(ary))
/* }}} */
/* print util {{{ */
template <class T> inline void print(const T &x) { cout << x << '\n'; }
template <class T> inline void printd(const T &x, int d) {
  cout << fixed << setprecision(d) << x << '\n';
}
template <class T> inline void printv(vec<T> &v) {
  int n = SZ(v);
  REP(i, n) cout << v[i] << "\n "[i < n - 1];
}
template <class T> inline void printv(vec<T> &v, int n) {
  REP(i, n) cout << v[i] << "\n "[i < n - 1];
}
template <class T> inline void printa(T *ary, int n) {
  REP(i, n) cout << ary[i] << "\n "[i < n - 1];
}
#define DUMP(x) cerr << #x << ": " << (x) << '\n'
#define DEBUG(x) cerr << #x << ": " << (x) << " (" << __LINE__ << ")" << '\n'
/* }}} */
/* template }}} */

int gcd(int a, int b) { return (b == 0 ? a : gcd(b, a % b)); }

signed main() {
  int n = in(), k = in();
  vi a = in(n);
  SORT(a);

  if (n == 1) {
    puts(a[0] == k ? "POSSIBLE" : "IMPOSSIBLE");
    return 0;
  } else if (a[n - 1] < k) {
    puts("IMPOSSIBLE");
    return 0;
  }

  int g = gcd(a[0], a[1]);
  FOR(i, 2, n) { g = gcd(g, a[i]); }

  for (int i : a) {
    if (abs(a[i] - k) % g == 0) {
      puts("POSSIBLE");
      return 0;
    }
  }
  puts("IMPOSSIBLE");

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

/* template {{{ */
/* vim: set foldmethod=marker: */
/* Roadagain {{{ */
/****************************************************************************************/
/*                                                                                      */
/*                                                                                      */
/*                                                                                      */
/*  /#######                            /##                               /## */
/* | ##__  ##                          | ##                              |__/ */
/* | ##  \ ##  /######   /######   /#######  /######   /######   /######  /##
 * /#######  */
/* | #######/ /##__  ## |____  ## /##__  ## |____  ## /##__  ## |____  ##| ##|
 * ##__  ## */
/* | ##__  ##| ##  \ ##  /#######| ##  | ##  /#######| ##  \ ##  /#######| ##|
 * ##  \ ## */
/* | ##  \ ##| ##  | ## /##__  ##| ##  | ## /##__  ##| ##  | ## /##__  ##| ##|
 * ##  | ## */
/* | ##  | ##|  ######/|  #######|  #######|  #######|  #######|  #######| ##|
 * ##  | ## */
/* |__/  |__/ \______/  \_______/ \_______/ \_______/ \____  ##
 * \_______/|__/|__/  |__/ */
/*                                                    /##  \ ## */
/*                                                   |  ######/ */
/*                                                    \______/ */
/*                                                                                      */
/****************************************************************************************/
/* }}} */
/* constant {{{ */
const int INF = (int)1e9;
const int MOD = (int)1e9 + 7;
const double PI = acos(-1);
const double EPS = 1e-14;
/* }}} */
/* alias {{{ */
template <class T> using vec = vector<T>;
using ll = long long;
using ull = unsigned long long;
using vi = vec<int>;
using vl = vec<ll>;
using vd = vec<double>;
using pii = pair<int, int>;
using pdd = pair<double, double>;
using vec2 = complex<double>;
/* }}} */
/* repetition {{{ */
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define RFOR(i, a, b) for (int i = (int)(b)-1; i >= (int)(a); --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define REPIT(i, obj) for (auto i = (obj).begin(); i != (obj).end(); ++i)
#define RREPIT(i, obj) for (auto i = (obj).rbegin(); i != (obj).rend(); ++i)
/* }}} */
/* short {{{ */
#define pb emplace_back
#define mp make_pair
#define fst first
#define sec second
/* }}} */
/* input {{{ */
template <class T = int> inline T in() {
  T x;
  cin >> x;
  return x;
}
template <class T = int> inline vec<T> in(int n) {
  vec<T> v(n);
  REP(i, n) v[i] = in<T>();
  return v;
}
template <class T = int> inline void in(T *x, int n) {
  REP(i, n) x[i] = in<T>();
}
#define inl in<ll>
#define ind in<double>
#define ins in<string>
/* }}} */
/* container util {{{ */
#define ALL(obj) (obj).begin(), (obj).end()
#define ALLA(ary, n) (ary), ((ary) + (n))
#define RALL(obj) (obj).rbegin(), (obj).rend()
#define SZ(obj) (obj).size()
#define SZA(ary) (sizeof(ary) / sizeof(*ary))
#define SORT(obj) sort(ALL(obj))
#define SORTA(ary, n) sort(ALLA(ary, n))
#define EXIST(obj, key) ((obj).find(key) != (obj).end())
#define CLEARY(ary) memset((ary), 0, sizeof(ary))
/* }}} */
/* print util {{{ */
template <class T> inline void print(const T &x) { cout << x << '\n'; }
template <class T> inline void printd(const T &x, int d) {
  cout << fixed << setprecision(d) << x << '\n';
}
template <class T> inline void printv(vec<T> &v) {
  int n = SZ(v);
  REP(i, n) cout << v[i] << "\n "[i < n - 1];
}
template <class T> inline void printv(vec<T> &v, int n) {
  REP(i, n) cout << v[i] << "\n "[i < n - 1];
}
template <class T> inline void printa(T *ary, int n) {
  REP(i, n) cout << ary[i] << "\n "[i < n - 1];
}
#define DUMP(x) cerr << #x << ": " << (x) << '\n'
#define DEBUG(x) cerr << #x << ": " << (x) << " (" << __LINE__ << ")" << '\n'
/* }}} */
/* template }}} */

int gcd(int a, int b) { return (b == 0 ? a : gcd(b, a % b)); }

signed main() {
  int n = in(), k = in();
  vi a = in(n);
  SORT(a);

  if (n == 1) {
    puts(a[0] == k ? "POSSIBLE" : "IMPOSSIBLE");
    return 0;
  } else if (a[n - 1] < k) {
    puts("IMPOSSIBLE");
    return 0;
  }

  int g = gcd(a[0], a[1]);
  FOR(i, 2, n) { g = gcd(g, a[i]); }

  for (int i : a) {
    if (abs(i - k) % g == 0) {
      puts("POSSIBLE");
      return 0;
    }
  }
  puts("IMPOSSIBLE");

  return 0;
}