Problem p03651 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define MAX_N 100001
#define INF_INT 2147483647
#define INF_LL 9223372036854775807
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long int ll;
typedef pair<ll, ll> P;
void init(int n);
int find(int n);
void unite(int x, int y);
bool same(int x, int y);
ll bpow(ll, ll, ll);
typedef vector<int> vec;
typedef vector<vec> mat;
mat mul(mat &A, mat &B);
mat pow(mat A, ll n);
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};

bool cmp_P(const P &a, const P &b) { return a.second < b.second; }
int main() {
  ll N, A[100001], K, mo = 0;
  cin >> N >> K;
  REP(i, N) cin >> A[i];
  sort(A, A + N);
  REP(i, N - 1) { mo = __gcd(A[i], A[i + 1]); }
  if (A[N - 1] >= K && K % mo == 0) {
    cout << "POSSIBLE" << endl;
  } else
    cout << "IMPOSSIBLE" << endl;

  return 0;
}

int par[MAX_N];
int ranks[MAX_N];

// n要素で初期化
void init(int n) {
  REP(i, n) {
    par[i] = i;
    ranks[i] = 0;
  }
}

// 木の根を求める
int find(int x) {
  if (par[x] == x) {
    return x;
  } else {
    return par[x] = find(par[x]);
  }
}

void unite(int x, int y) {
  x = find(x);
  y = find(y);
  if (x == y)
    return;
  if (ranks[x] < ranks[y]) {
    par[x] = y;
  } else {
    par[y] = x;
    if (ranks[x] == ranks[y])
      ranks[x]++;
  }
}

bool same(int x, int y) { return find(x) == find(y); }

ll bpow(ll a, ll n, ll mod) {
  int i = 0;
  ll res = 1;
  while (n) {
    if (n & 1)
      res = (res * a) % mod;
    a = (a * a) % mod;
    n >>= 1;
  }
  return res;
}
const int MOD = 1000000007;
mat mul(mat &A, mat &B) {
  mat C(A.size(), vec(B[0].size()));
  REP(i, A.size()) REP(k, B.size()) REP(j, B[0].size()) {
    C[i][j] = (C[i][j] + A[i][k] * B[k][j]) % MOD;
  }
  return C;
}

mat pow(mat A, ll n) {
  mat B(A.size(), vec(A.size()));
  REP(i, A.size()) { B[i][i] = 1; }
  while (n > 0) {
    if (n & 1)
      B = mul(B, A);
    A = mul(A, A);
    n >>= 1;
  }
  return B;
}


Fixed submission:
#include <bits/stdc++.h>
#define MAX_N 100001
#define INF_INT 2147483647
#define INF_LL 9223372036854775807
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long int ll;
typedef pair<ll, ll> P;
void init(int n);
int find(int n);
void unite(int x, int y);
bool same(int x, int y);
ll bpow(ll, ll, ll);
typedef vector<int> vec;
typedef vector<vec> mat;
mat mul(mat &A, mat &B);
mat pow(mat A, ll n);
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};

bool cmp_P(const P &a, const P &b) { return a.second < b.second; }
int main() {
  ll N, A[100001], K, mo = 0;
  cin >> N >> K;
  REP(i, N) cin >> A[i];
  sort(A, A + N);
  REP(i, N) {
    if (A[i] == K) {
      cout << "POSSIBLE" << endl;
      return 0;
    }
  }
  if (N == 1) {
    cout << "IMPOSSIBLE" << endl;
    return 0;
  }
  mo = A[0];
  REP(i, N - 1) { mo = __gcd(mo, A[i + 1]); }
  if (A[N - 1] >= K && K % mo == 0) {
    cout << "POSSIBLE" << endl;
  } else
    cout << "IMPOSSIBLE" << endl;

  return 0;
}

int par[MAX_N];
int ranks[MAX_N];

// n要素で初期化
void init(int n) {
  REP(i, n) {
    par[i] = i;
    ranks[i] = 0;
  }
}

// 木の根を求める
int find(int x) {
  if (par[x] == x) {
    return x;
  } else {
    return par[x] = find(par[x]);
  }
}

void unite(int x, int y) {
  x = find(x);
  y = find(y);
  if (x == y)
    return;
  if (ranks[x] < ranks[y]) {
    par[x] = y;
  } else {
    par[y] = x;
    if (ranks[x] == ranks[y])
      ranks[x]++;
  }
}

bool same(int x, int y) { return find(x) == find(y); }

ll bpow(ll a, ll n, ll mod) {
  int i = 0;
  ll res = 1;
  while (n) {
    if (n & 1)
      res = (res * a) % mod;
    a = (a * a) % mod;
    n >>= 1;
  }
  return res;
}
const int MOD = 1000000007;
mat mul(mat &A, mat &B) {
  mat C(A.size(), vec(B[0].size()));
  REP(i, A.size()) REP(k, B.size()) REP(j, B[0].size()) {
    C[i][j] = (C[i][j] + A[i][k] * B[k][j]) % MOD;
  }
  return C;
}

mat pow(mat A, ll n) {
  mat B(A.size(), vec(A.size()));
  REP(i, A.size()) { B[i][i] = 1; }
  while (n > 0) {
    if (n & 1)
      B = mul(B, A);
    A = mul(A, A);
    n >>= 1;
  }
  return B;
}