Problem p02793 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define repr(i, from, to) for (int(i) = (from); (i) < (to); (i)++)
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
// const bool debug=true;
const bool debug = false;
#define DEBUG if (debug == true)
#define vprint(x)                                                              \
  for (auto a : (x))                                                           \
    cout << x << endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll MOD = 1000000007;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

class ModCom {
public:
  ModCom(int _n, long long _mod) {
    assert(_n >= 2);
    n = _n + 1;
    mod = _mod;
    fac.assign(n, 0);
    finv.assign(n, 0);
    inv.assign(n, 0);
    init();
  }
  vector<long long> inv;
  vector<long long> fac;
  vector<long long> finv;

  long long com(int _n, int k) {
    if (_n < k) {
      return 0;
    }
    if (_n < 0 || k < 0) {
      return 0;
    }
    return fac.at(_n) * (finv.at(k) * finv.at(_n - k) % mod) % mod;
  }

private:
  int n;
  long long mod;

  void init(void) {
    fac.at(0) = fac.at(1) = 1;
    finv.at(0) = finv.at(1) = 1;
    inv.at(1) = 1;
    for (int i = 2; i < n; i++) {
      fac.at(i) = fac.at(i - 1) * i % mod;
      inv.at(i) = mod - inv.at(mod % i) * (mod / i) % mod;
      finv.at(i) = finv.at(i - 1) * inv.at(i) % mod;
    }
    return;
  }
};

ModCom com(int(1e+6) + 200, MOD);

long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

vector<long long> eratosthenes(long long n) {
  vector<long long> ret;
  vector<bool> check(n + 100, false);
  if (n < 2) {
    return ret;
  }
  long long idx = 2;
  while (idx * idx <= n) {
    if (!check[idx]) {
      ret.push_back(idx);
      for (int i = idx; i <= n; i += idx) {
        check[i] = true;
      }
    }
  }
  for (int i = idx; i <= n; i++) {
    if (!check[i]) {
      ret.push_back(i);
    }
  }
  return ret;
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n;
  cin >> n;
  vector<ll> a(n);
  vector<ll> ps = eratosthenes(1000000 + 10);
  vector<ll> mp(1000000 + 10, 0);
  rep(i, n) cin >> a[i];
  rep(i, n) {
    ll target = a[i];
    for (auto x : ps) {
      ll cnt = 0;
      if (x * x > a[i])
        break;
      while (target % x == 0) {
        cnt++;
        target /= x;
      }
      chmax(mp[x], cnt);
    }
    if (target != 1) {
      chmax(mp[target], 1LL);
    }
  }
  ll lcm = 1;
  rep(i, 1000000 + 10) {
    if (mp[i] == 0)
      continue;
    lcm *= modpow(i, mp[i], MOD);
    lcm %= MOD;
  }
  ll res = 0;
  rep(i, n) {
    res += lcm * com.inv[a[i]];
    res %= MOD;
  }
  cout << res << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define repr(i, from, to) for (int(i) = (from); (i) < (to); (i)++)
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
// const bool debug=true;
const bool debug = false;
#define DEBUG if (debug == true)
#define vprint(x)                                                              \
  for (auto a : (x))                                                           \
    cout << x << endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll MOD = 1000000007;
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

class ModCom {
public:
  ModCom(int _n, long long _mod) {
    assert(_n >= 2);
    n = _n + 1;
    mod = _mod;
    fac.assign(n, 0);
    finv.assign(n, 0);
    inv.assign(n, 0);
    init();
  }
  vector<long long> inv;
  vector<long long> fac;
  vector<long long> finv;

  long long com(int _n, int k) {
    if (_n < k) {
      return 0;
    }
    if (_n < 0 || k < 0) {
      return 0;
    }
    return fac.at(_n) * (finv.at(k) * finv.at(_n - k) % mod) % mod;
  }

private:
  int n;
  long long mod;

  void init(void) {
    fac.at(0) = fac.at(1) = 1;
    finv.at(0) = finv.at(1) = 1;
    inv.at(1) = 1;
    for (int i = 2; i < n; i++) {
      fac.at(i) = fac.at(i - 1) * i % mod;
      inv.at(i) = mod - inv.at(mod % i) * (mod / i) % mod;
      finv.at(i) = finv.at(i - 1) * inv.at(i) % mod;
    }
    return;
  }
};

ModCom com(int(1e+6) + 200, MOD);

long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

vector<long long> eratosthenes(long long n) {
  vector<long long> ret;
  vector<bool> check(n + 100, false);
  if (n < 2) {
    return ret;
  }
  long long idx = 2;
  while (idx * idx <= n) {
    if (!check[idx]) {
      ret.push_back(idx);
      for (int i = idx; i <= n; i += idx) {
        check[i] = true;
      }
    }
    idx++;
  }
  for (int i = idx; i <= n; i++) {
    if (!check[i]) {
      ret.push_back(i);
    }
  }
  return ret;
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n;
  cin >> n;
  vector<ll> a(n);
  vector<ll> ps = eratosthenes(1000000 + 10);
  vector<ll> mp(1000000 + 10, 0);
  rep(i, n) cin >> a[i];
  rep(i, n) {
    ll target = a[i];
    for (auto x : ps) {
      ll cnt = 0;
      if (x * x > a[i])
        break;
      while (target % x == 0) {
        cnt++;
        target /= x;
      }
      chmax(mp[x], cnt);
    }
    if (target != 1) {
      chmax(mp[target], 1LL);
    }
  }
  ll lcm = 1;
  rep(i, 1000000 + 10) {
    if (mp[i] == 0)
      continue;
    lcm *= modpow(i, mp[i], MOD);
    lcm %= MOD;
  }
  ll res = 0;
  rep(i, n) {
    res += lcm * com.inv[a[i]];
    res %= MOD;
  }
  cout << res << endl;
  return 0;
}