Problem p02548 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll, ll>
#define FOR(I, A, B) for (ll I = ll(A); I < ll(B); ++I)
#define FORR(I, A, B) for (ll I = ll((B)-1); I >= ll(A); --I)
#define TO(x, t, f) ((x) ? (t) : (f))
#define SORT(x) (sort(x.begin(), x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x, v)                                                             \
  (lower_bound(x.begin(), x.end(), v) - x.begin()) // xi>=v  x is sorted
#define POSU(x, v)                                                             \
  (upper_bound(x.begin(), x.end(), v) - x.begin()) // xi>v  x is sorted
#define NUM(x, v) (POSU(x, v) - POSL(x, v))        // x is sorted
#define REV(x) (reverse(x.begin(), x.end()))       // reverse
ll gcd_(ll a, ll b) {
  if (a % b == 0)
    return b;
  return gcd_(b, a % b);
}
ll lcm_(ll a, ll b) {
  ll c = gcd_(a, b);
  return ((a / c) * b);
}
#define NEXTP(x) next_permutation(x.begin(), x.end())
const ll INF = ll(1e16) + ll(7);
const ll MOD = 1000000007LL;
#define out(a) cout << fixed << setprecision((a))
// tie(a,b,c) = make_tuple(10,9,87);
#define pop_(a) __builtin_popcount((a))
ll keta(ll a) {
  ll r = 0;
  while (a) {
    a /= 10;
    r++;
  }
  return r;
}

template <typename T> class Seg_Tree {
public: // 0-index
  vector<T> dat;
  T initial, M;
  int n;
  T unite(T a, T b) { //
    return a + b;
  }
  Seg_Tree(int n0_ = 1, T initial_ = 1, T M_ = 1) {
    initsize(n0_, initial_, M_);
  }
  void initsize(int n0, T initial_, T M_) {
    M = M_;
    initial = initial_;
    int k = 1;
    while (1) {
      if (n0 <= k) {
        n = k;
        dat.resize(2 * n - 1);
        for (int i = 0; i < 2 * n - 1; i++)
          dat[i] = initial;
        break;
      }
      k *= 2;
    }
  }

  // i banme wo x nisuru
  void update(int i, T x) {
    i += n - 1;
    dat[i] = x;
    while (i > 0) {
      i = (i - 1) / 2;
      dat[i] = unite(dat[i * 2 + 1], dat[i * 2 + 2]);
    }
  }

  //[a,b)
  T query0(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return initial;
    if (a <= l && r <= b)
      return dat[k];
    else {
      T vl = query0(a, b, k * 2 + 1, l, (l + r) / 2);
      T vr = query0(a, b, k * 2 + 2, (l + r) / 2, r);
      return unite(vl, vr);
    }
  }

  // return [a,b)
  T query(int a, int b) { return query0(a, b, 0, 0, n); }
};

vector<ll> enum_div(ll n) { // yakusu
  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);
    }
  }
  return ret;
}

map<ll, ll> soinsubunkai(ll x) { // x = {first^second}*...
  map<ll, ll> ans;
  if (x == 1) {
    ans[1]++;
    return ans;
  }
  ll p = x;
  for (ll i = 2; i * i <= x; i++) {
    while (p % i == 0) {
      p /= i;
      ans[i]++;
    }
  }
  if (p != 1)
    ans[p]++;
  return ans;
}

int main() {

  ll N;

  cin >> N;

  ll ans = 0;

  FOR(c, 1, N) {
    ll k = N - c;
    for (ll i = 1; i * i <= k; ++i) {
      if (k % i == 0) {
        ans++;
        if (i * i != k)
          ans++;
      }
    }
  }

  cout << ans << endl;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll, ll>
#define FOR(I, A, B) for (ll I = ll(A); I < ll(B); ++I)
#define FORR(I, A, B) for (ll I = ll((B)-1); I >= ll(A); --I)
#define TO(x, t, f) ((x) ? (t) : (f))
#define SORT(x) (sort(x.begin(), x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x, v)                                                             \
  (lower_bound(x.begin(), x.end(), v) - x.begin()) // xi>=v  x is sorted
#define POSU(x, v)                                                             \
  (upper_bound(x.begin(), x.end(), v) - x.begin()) // xi>v  x is sorted
#define NUM(x, v) (POSU(x, v) - POSL(x, v))        // x is sorted
#define REV(x) (reverse(x.begin(), x.end()))       // reverse
ll gcd_(ll a, ll b) {
  if (a % b == 0)
    return b;
  return gcd_(b, a % b);
}
ll lcm_(ll a, ll b) {
  ll c = gcd_(a, b);
  return ((a / c) * b);
}
#define NEXTP(x) next_permutation(x.begin(), x.end())
const ll INF = ll(1e16) + ll(7);
const ll MOD = 1000000007LL;
#define out(a) cout << fixed << setprecision((a))
// tie(a,b,c) = make_tuple(10,9,87);
#define pop_(a) __builtin_popcount((a))
ll keta(ll a) {
  ll r = 0;
  while (a) {
    a /= 10;
    r++;
  }
  return r;
}

template <typename T> class Seg_Tree {
public: // 0-index
  vector<T> dat;
  T initial, M;
  int n;
  T unite(T a, T b) { //
    return a + b;
  }
  Seg_Tree(int n0_ = 1, T initial_ = 1, T M_ = 1) {
    initsize(n0_, initial_, M_);
  }
  void initsize(int n0, T initial_, T M_) {
    M = M_;
    initial = initial_;
    int k = 1;
    while (1) {
      if (n0 <= k) {
        n = k;
        dat.resize(2 * n - 1);
        for (int i = 0; i < 2 * n - 1; i++)
          dat[i] = initial;
        break;
      }
      k *= 2;
    }
  }

  // i banme wo x nisuru
  void update(int i, T x) {
    i += n - 1;
    dat[i] = x;
    while (i > 0) {
      i = (i - 1) / 2;
      dat[i] = unite(dat[i * 2 + 1], dat[i * 2 + 2]);
    }
  }

  //[a,b)
  T query0(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return initial;
    if (a <= l && r <= b)
      return dat[k];
    else {
      T vl = query0(a, b, k * 2 + 1, l, (l + r) / 2);
      T vr = query0(a, b, k * 2 + 2, (l + r) / 2, r);
      return unite(vl, vr);
    }
  }

  // return [a,b)
  T query(int a, int b) { return query0(a, b, 0, 0, n); }
};

vector<ll> enum_div(ll n) { // yakusu
  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);
    }
  }
  return ret;
}

map<ll, ll> soinsubunkai(ll x) { // x = {first^second}*...
  map<ll, ll> ans;
  if (x == 1) {
    ans[1]++;
    return ans;
  }
  ll p = x;
  for (ll i = 2; i * i <= x; i++) {
    while (p % i == 0) {
      p /= i;
      ans[i]++;
    }
  }
  if (p != 1)
    ans[p]++;
  return ans;
}

int main() {

  ll N;

  cin >> N;

  ll ans = 0;

  FOR(a, 1, N) {
    ll b_max = N / a;
    if (b_max * a == N)
      b_max--;
    ans += b_max;
  }

  cout << ans << endl;
}