Problem p02624 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
             tree_order_statistics_node_update>
    oset;
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
using ll = long long;
#define int ll
ll n;

void findDivisors(ll n) {
  vector<ll> div(n + 5);
  for (ll i = 1; i <= n; i++) {
    for (ll j = 1; j * i <= n; j++)
      div[i * j]++;
  }
  ll ans = 0;
  for (ll i = 1; i <= n; i++)
    ans += (ll)i * (ll)div[i];
  cout << ans;
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n;
  findDivisors(n);
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
             tree_order_statistics_node_update>
    oset;
#define sim template <class c
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \\
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \\
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << endl; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
using ll = long long;

const int N = 10000000;
vector<vector<int>> divisors(N + 2);
int n;

void test_case() {
  ll ans = 0;
  for (ll i = 1; i <= n; i++) {
    ans += i * ((ll)divisors[i].size() + 1);
  }
  cout << ans;
  return;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n;
  for (int i = 2; i <= n; i++) {
    for (int j = i; j <= n; j += i) {
      divisors[j].push_back(i);
    }
  }
  int T = 1;
  while (T--) {
    test_case();
  }
  return 0;
}