Problem p02548 (C++) — buggy submission, verdict: Time Limit Exceeded

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

#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define all(x) (x).begin(), (x).end()
using ll = long long;
using P = pair<ll, ll>;
string char_to_string(char val) { return string(1, val); }
int char_to_int(char val) { return val - '0'; }
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;
}
struct edge {
  ll to, cost;
};

// Sieve of Eratosthenes
// (*this)[i] = (divisor of i, greater than 1)
// Example: [0, 1, 2, 3, 2, 5, 3, 7, 2, 3, 2, 11, ...]
// Complexity: Space O(MAXN), Time (construction) O(MAXNloglogMAXN)
struct SieveOfEratosthenes : std::vector<int> {
  std::vector<int> primes;
  SieveOfEratosthenes(int MAXN) : std::vector<int>(MAXN + 1) {
    std::iota(begin(), end(), 0);
    for (int i = 2; i <= MAXN; i++) {
      if ((*this)[i] == i) {
        primes.push_back(i);
        for (int j = i; j <= MAXN; j += i)
          (*this)[j] = i;
      }
    }
  }
  using T = long long int;
  // Prime factorization for x <= MAXN^2
  // Complexity: O(log x)          (x <= MAXN)
  //             O(MAXN / logMAXN) (MAXN < x <= MAXN^2)
  std::map<T, int> Factorize(T x) {
    assert(x <= 1LL * (int(size()) - 1) * (int(size()) - 1));
    std::map<T, int> ret;
    if (x < int(size())) {
      while (x > 1) {
        ret[(*this)[x]]++;
        x /= (*this)[x];
      }
    } else {
      for (auto p : primes) {
        while (!(x % p))
          x /= p, ret[p]++;
        if (x == 1)
          break;
      }
      if (x > 1)
        ret[x]++;
    }
    return ret;
  }
  std::vector<T> Divisors(T x) {
    std::vector<T> ret{1};
    for (auto p : Factorize(x)) {
      int n = ret.size();
      for (int i = 0; i < n; i++) {
        for (T a = 1, d = 1; d <= p.second; d++) {
          a *= p.first;
          ret.push_back(ret[i] * a);
        }
      }
    }
    return ret; // Not sorted
  }
  // Moebius function Table
  // return: [0=>0, 1=>1, 2=>-1, 3=>-1, 4=>0, 5=>-1, 6=>1, 7=>-1, 8=>0, ...]
  std::vector<int> GenerateMoebiusFunctionTable() {
    std::vector<int> ret(size());
    for (int i = 1; i < int(size()); i++) {
      if (i == 1)
        ret[i] = 1;
      else if ((i / (*this)[i]) % (*this)[i] == 0)
        ret[i] = 0;
      else
        ret[i] = -ret[i / (*this)[i]];
    }
    return ret;
  }
};
SieveOfEratosthenes sieve(1000000);

int main() {
  int N;
  cin >> N;
  ll ans = 0;
  for (int i = 1; i < N; ++i) {
    int tmp = N - i;
    auto x = sieve.Divisors(tmp);
    ans += x.size();
  }
  cout << ans << endl;
}

Error: TLE

Fixed submission:

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

#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define all(x) (x).begin(), (x).end()
using ll = long long;
using P = pair<ll, ll>;
string char_to_string(char val) { return string(1, val); }
int char_to_int(char val) { return val - '0'; }
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;
}
struct edge {
  ll to, cost;
};

vector<ll> divisor(ll n) {
  vector<ll> ret;
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }

  sort(begin(ret), end(ret));
  return (ret);
}

int main() {
  int N;
  cin >> N;
  ll ans = 0;
  for (int i = 1; i < N; ++i) {
    int tmp = N - i;
    auto x = divisor(tmp);
    ans += x.size();
  }
  cout << ans << endl;
}