Problem p02814 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define rep(i, N) for (int i = 0, i##_max = (N); i < i##_max; ++i)
#define repp(i, l, r) for (int i = (l), i##_max = (r); i < i##_max; ++i)
#define per(i, N) for (int i = (N)-1; i >= 0; --i)
#define perr(i, l, r) for (int i = r - 1, i##_min(l); i >= i##_min; --i)
#define all(arr) (arr).begin(), (arr).end()
#define SP << " " <<
#define SPF << " "
#define SPEEDUP                                                                \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);
#define MAX_I INT_MAX      // 1e9
#define MIN_I INT_MIN      //-1e9
#define MAX_UI UINT_MAX    // 1e9
#define MAX_LL LLONG_MAX   // 1e18
#define MIN_LL LLONG_MIN   //-1e18
#define MAX_ULL ULLONG_MAX // 1e19
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<char, char> PCC;
typedef pair<ll, ll> PLL;
typedef pair<char, int> PCI;
typedef pair<int, char> PIC;
typedef pair<ll, int> PLI;
typedef pair<int, ll> PIL;
typedef pair<ll, char> PLC;
typedef pair<char, ll> PCL;

inline void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
inline void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
inline void Yay(bool b) { cout << (b ? "Yay!" : ":(") << endl; }

ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

int fac2(ll x) {
  int count = 0;
  while (x % 2 == 0) {
    x <<= 1;
    ++count;
  }
  return count;
}

int main(void) {
  SPEEDUP
  cout << setprecision(15);
  int N;
  ll M;
  cin >> N >> M;

  vector<ll> v(N);
  rep(i, N) cin >> v[i], v[i] = v[i] / 2;
  int fac20 = fac2(v[N - 1]);
  rep(i, N - 1) {
    if (fac2(v[i]) != fac20) {
      cout << 0 << endl;
      return 0;
    }
  }
  ll LCM = 1ll;
  rep(i, N) {
    ll GCD = gcd(LCM, v[i]);
    LCM = LCM / GCD * v[i];
    if (LCM > M) {
      cout << 0 << endl;
      return 0;
    }
  }
  ll num = M / LCM;
  cout << (num + 1ll) / 2ll << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define rep(i, N) for (int i = 0, i##_max = (N); i < i##_max; ++i)
#define repp(i, l, r) for (int i = (l), i##_max = (r); i < i##_max; ++i)
#define per(i, N) for (int i = (N)-1; i >= 0; --i)
#define perr(i, l, r) for (int i = r - 1, i##_min(l); i >= i##_min; --i)
#define all(arr) (arr).begin(), (arr).end()
#define SP << " " <<
#define SPF << " "
#define SPEEDUP                                                                \
  cin.tie(0);                                                                  \
  ios::sync_with_stdio(false);
#define MAX_I INT_MAX      // 1e9
#define MIN_I INT_MIN      //-1e9
#define MAX_UI UINT_MAX    // 1e9
#define MAX_LL LLONG_MAX   // 1e18
#define MIN_LL LLONG_MIN   //-1e18
#define MAX_ULL ULLONG_MAX // 1e19
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<char, char> PCC;
typedef pair<ll, ll> PLL;
typedef pair<char, int> PCI;
typedef pair<int, char> PIC;
typedef pair<ll, int> PLI;
typedef pair<int, ll> PIL;
typedef pair<ll, char> PLC;
typedef pair<char, ll> PCL;

inline void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
inline void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
inline void Yay(bool b) { cout << (b ? "Yay!" : ":(") << endl; }

ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

int fac2(ll x) {
  int count = 0;
  while (x % 2 == 0) {
    x >>= 1;
    ++count;
  }
  return count;
}

int main(void) {
  SPEEDUP
  cout << setprecision(15);
  int N;
  ll M;
  cin >> N >> M;

  vector<ll> v(N);
  rep(i, N) cin >> v[i], v[i] = v[i] / 2;
  int fac20 = fac2(v[N - 1]);
  rep(i, N - 1) {
    if (fac2(v[i]) != fac20) {
      cout << 0 << endl;
      return 0;
    }
  }
  ll LCM = 1ll;
  rep(i, N) {
    ll GCD = gcd(LCM, v[i]);
    LCM = LCM / GCD * v[i];
    if (LCM > M) {
      cout << 0 << endl;
      return 0;
    }
  }
  ll num = M / LCM;
  cout << (num + 1ll) / 2ll << endl;
  return 0;
}