Problem p02548 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef int itn;
const ll LINF = 1e18;
const int INF = 1e9;

// マクロ定義
#define vvint(vec, n, m, l)                                                    \
  vector<vector<int>> vec(n, vector<int>(m, l)); // lで初期化
#define vvll(vec, n, m, l) vector<vector<ll>> vec(n, vector<ll>(m, l));
#define vint vector<int>
#define pint pair<int, int>
#define rep(i, a) for (ll i = 0; i < (a); i++)
#define all(x) (x).begin(), (x).end()
#define debug system("pause") // デバッグ用
#define ret return 0

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

using Graph = vector<vector<ll>>;

#define ketasitei setprecision(15) // 15桁表示

const ll MOD = 1000000007;
const double PI = 3.1415926535897932;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << ketasitei;

  ll n;
  cin >> n;
  ll ans = 0;
  for (ll c = 1; c <= n; c++) {
    for (ll a = 1; a * a <= n - c; a++) {
      ll b = (n - c) / a;
      if (a * b + c == n) {
        if (a == b)
          ans++;
        else
          ans += 2;
      }
    }
  }
  cout << ans << endl;

  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef int itn;
const ll LINF = 1e18;
const int INF = 1e9;

// マクロ定義
#define vvint(vec, n, m, l)                                                    \
  vector<vector<int>> vec(n, vector<int>(m, l)); // lで初期化
#define vvll(vec, n, m, l) vector<vector<ll>> vec(n, vector<ll>(m, l));
#define vint vector<int>
#define pint pair<int, int>
#define rep(i, a) for (ll i = 0; i < (a); i++)
#define all(x) (x).begin(), (x).end()
#define debug system("pause") // デバッグ用
#define ret return 0

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

using Graph = vector<vector<ll>>;

#define ketasitei setprecision(15) // 15桁表示

const ll MOD = 1000000007;
const double PI = 3.1415926535897932;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << ketasitei;

  ll n;
  cin >> n;
  ll ans = 0;
  for (ll a = 1; a <= n; a++) {
    ll b = n / a;
    if (a * b == n)
      ans += max(0LL, b - 1);
    else
      ans += b;
  }
  cout << ans << endl;

  return 0;
}