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) < (n); (i)++)
#define rrep(i, n) for (int(i) = ((n)-1); (i) >= 0; (i)--)
#define int long long
#define miele(v) min_element(v.begin(), v.end())
#define maele(v) max_element(v.begin(), v.end())
#define SUM(v) accumulate(v.begin(), v.end(), 0LL)
#define lb(a, key) lower_bound(a.begin(), a.end(), key)
#define ub(a, key) upper_bound(a.begin(), a.end(), key)
#define COUNT(a, key) count(a.begin(), a.end(), key)
#define BITCOUNT(x) __builtin_popcount(x)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
using P = pair<int, int>;
using WeightedGraph = vector<vector<P>>;
using UnWeightedGraph = vector<vector<int>>;
using Real = long double;
using Point = complex<Real>; // Point and Vector2d is the same!
using Vector2d = complex<Real>;
const long long INF = 1LL << 60;
const int MOD = 1000000007;
const double EPS = 1e-15;
const double PI = 3.14159265358979323846;
template <typename T> int getIndexOfLowerBound(vector<T> &v, T x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <typename T> int getIndexOfUpperBound(vector<T> &v, T x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
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;
}
#define DUMPOUT cerr
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
istream &operator>>(istream &is, Point &p) {
  Real a, b;
  is >> a >> b;
  p = Point(a, b);
  return is;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p_var) {
  is >> p_var.first >> p_var.second;
  return is;
}
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  DUMPOUT << '{';
  os << pair_var.first;
  DUMPOUT << ',';
  os << " " << pair_var.second;
  DUMPOUT << '}';
  return os;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  DUMPOUT << '[';
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  DUMPOUT << ']';
  return os;
}
template <typename T> ostream &operator<<(ostream &os, vector<vector<T>> &df) {
  for (auto &vec : df)
    os << vec;
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  DUMPOUT << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      DUMPOUT << ", ";
    itr--;
  }
  DUMPOUT << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  DUMPOUT << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      DUMPOUT << ", ";
    itr--;
  }
  DUMPOUT << "}";
  return os;
}
void print() { cout << endl; }
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail) != 0)
    cout << " ";
  print(forward<Tail>(tail)...);
}
void dump_func() { DUMPOUT << '#' << endl; }
template <typename Head, typename... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0)
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int ans = 0;

  for (int i = 1; i <= n - 1; i++) {
    int l = -1, r = 1000000; // l,rの範囲にめっちゃ注意!
    while (abs(l - r) > 1) {
      int mid = l + (r - l) / 2;
      if (mid * i < n)
        l = mid;
      else
        r = mid;
    }
    ans += l;
    // dump(l, i);
  }
  print(ans);
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define rrep(i, n) for (int(i) = ((n)-1); (i) >= 0; (i)--)
#define itn int
#define miele(v) min_element(v.begin(), v.end())
#define maele(v) max_element(v.begin(), v.end())
#define SUM(v) accumulate(v.begin(), v.end(), 0LL)
#define lb(a, key) lower_bound(a.begin(), a.end(), key)
#define ub(a, key) upper_bound(a.begin(), a.end(), key)
#define COUNT(a, key) count(a.begin(), a.end(), key)
#define BITCOUNT(x) __builtin_popcount(x)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
using P = pair<int, int>;
using WeightedGraph = vector<vector<P>>;
using UnWeightedGraph = vector<vector<int>>;
using Real = long double;
using Point = complex<Real>; // Point and Vector2d is the same!
using Vector2d = complex<Real>;
const long long INF = 1LL << 60;
const int MOD = 1000000007;
const double EPS = 1e-15;
const double PI = 3.14159265358979323846;
template <typename T> int getIndexOfLowerBound(vector<T> &v, T x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <typename T> int getIndexOfUpperBound(vector<T> &v, T x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
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;
}
#define DUMPOUT cerr
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
istream &operator>>(istream &is, Point &p) {
  Real a, b;
  is >> a >> b;
  p = Point(a, b);
  return is;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p_var) {
  is >> p_var.first >> p_var.second;
  return is;
}
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec)
    is >> x;
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  DUMPOUT << '{';
  os << pair_var.first;
  DUMPOUT << ',';
  os << " " << pair_var.second;
  DUMPOUT << '}';
  return os;
}
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  DUMPOUT << '[';
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  DUMPOUT << ']';
  return os;
}
template <typename T> ostream &operator<<(ostream &os, vector<vector<T>> &df) {
  for (auto &vec : df)
    os << vec;
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  DUMPOUT << "{";
  repi(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end())
      DUMPOUT << ", ";
    itr--;
  }
  DUMPOUT << "}";
  return os;
}
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  DUMPOUT << "{";
  repi(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end())
      DUMPOUT << ", ";
    itr--;
  }
  DUMPOUT << "}";
  return os;
}
void print() { cout << endl; }
template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail) != 0)
    cout << " ";
  print(forward<Tail>(tail)...);
}
void dump_func() { DUMPOUT << '#' << endl; }
template <typename Head, typename... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0)
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \\
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                              \\
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl  \\
          << "    ",                                                           \\
      dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

template <typename T> T power(T x, int n) {
  T ret = 1;
  while (n > 0) {
    if (n & 1)
      (ret *= x);
    (x *= x);
    n >>= 1;
  }
  return ret;
}

int DIV(int n) {
  int cnt = 0;
  for (int i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      cnt++;
      if (i * i != n)
        cnt++;
    }
  }

  return (cnt);
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int ans = 0;
  for (int j = 1; j <= n - 1; ++j) {
    for (int i = 1; i * i <= j; ++i) {
      if (j % i == 0) {
        ans++;
        if (i * i != j)
          ans++;
      }
    }
  }
  cout << ans << '\\n';
}