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

#include <bits/stdc++.h>

using namespace std;
#define ll long long
#define ld long double
#define pll pair<long long, long long>
#define vll vector<long long>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define deb(x) cout << #x << "=" << x << endl
#define F(i, a, b) for (ll i = a; i <= b; i++)
#define RF(i, a, b) for (ll i = a; i >= b; i--)
#define in(a, n) F(i, 0, n - 1) cin >> a[i]
#define vi vector<int>
#define out(a, n)                                                              \\
  F(i, 0, n - 1) cout << a[i] << " ";                                          \\
  cout << endl
#define mod 998244353
#define trace1(x) cerr << #x << ": " << x << endl
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl
#define trace3(x, y, z)                                                        \\
  cerr << #x << ":" << x << " | " << #y << ": " << y << " | " << #z << ": "    \\
       << z << endl
#define trace4(a, b, c, d)                                                     \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << endl
#define trace5(a, b, c, d, e)                                                  \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl
#define trace6(a, b, c, d, e, f)                                               \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \\
       << #f << ": " << f << endl
#define int long long
set<ll> primes;
const int N = 1e7 + 5;
vector<int> v[N];
void Sieve(ll n) {
  bool prime[n + 1];
  for (ll i = 0; i < n + 1; ++i)
    prime[i] = true;
  for (ll p = 2; p * p <= n; ++p) {
    if (prime[p] == true) {
      for (ll i = 2 * p; i <= n; i += p) {
        prime[i] = false;
        v[i].pb(p);
      }
    }
  }
  for (ll p = 2; p <= n; p++)
    if (prime[p])
      primes.insert(p);
}

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);

  int t = 1;
  // cin>>t;
  while (t--) {
    int n;
    cin >> n;

    int ans = 0;

    vector<int> f(N);
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j * i <= n; j++)
        f[i * j]++;

      ans += i * f[i];
    }
    cout << ans;
  }
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>

using namespace std;
#define ll long long
#define ld long double
#define pll pair<long long, long long>
#define vll vector<long long>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define deb(x) cout << #x << "=" << x << endl
#define F(i, a, b) for (ll i = a; i <= b; i++)
#define RF(i, a, b) for (ll i = a; i >= b; i--)
#define in(a, n) F(i, 0, n - 1) cin >> a[i]
#define vi vector<int>
#define out(a, n)                                                              \\
  F(i, 0, n - 1) cout << a[i] << " ";                                          \\
  cout << endl
#define mod 998244353
#define trace1(x) cerr << #x << ": " << x << endl
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl
#define trace3(x, y, z)                                                        \\
  cerr << #x << ":" << x << " | " << #y << ": " << y << " | " << #z << ": "    \\
       << z << endl
#define trace4(a, b, c, d)                                                     \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << endl
#define trace5(a, b, c, d, e)                                                  \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl
#define trace6(a, b, c, d, e, f)                                               \\
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \\
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \\
       << #f << ": " << f << endl
#define int long long
set<ll> primes;

// int n,m;

int ans;
vector<int> d;
vector<vector<int>> v;
vector<int> par;
vector<int> tin, tout;

void dfs(int u, int p, int dep) {
  // cout<<"h\\n";
  // trace3(u,p,dep);
  par[u] = p;
  d[u] = dep;
  tin[u] = ++ans;
  for (auto x : v[u]) {
    if (x == p)
      continue;

    dfs(x, u, dep + 1);
  }
  tout[u] = ++ans;
}

bool isancesstor(int u, int v) {
  return (tin[u] <= tin[v] and tout[u] >= tout[v]);
}
void SieveOfEratosthenes(int n, bool prime[], bool primesquare[], int a[]) {
  // Create a boolean array "prime[0..n]" and
  // initialize all entries it as true. A value
  // in prime[i] will finally be false if i is
  // Not a prime, else true.
  for (int i = 2; i <= n; i++)
    prime[i] = true;

  // Create a boolean array "primesquare[0..n*n+1]"
  // and initialize all entries it as false. A value
  // in squareprime[i] will finally be true if i is
  // square of prime, else false.
  for (int i = 0; i <= (n * n + 1); i++)
    primesquare[i] = false;

  // 1 is not a prime number
  prime[1] = false;

  for (int p = 2; p * p <= n; p++) {
    // If prime[p] is not changed, then
    // it is a prime
    if (prime[p] == true) {
      // Update all multiples of p
      for (int i = p * 2; i <= n; i += p)
        prime[i] = false;
    }
  }

  int j = 0;
  for (int p = 2; p <= n; p++) {
    if (prime[p]) {
      // Storing primes in an array
      a[j] = p;

      // Update value in primesquare[p*p],
      // if p is prime.
      primesquare[p * p] = true;
      j++;
    }
  }
}

// Function to count divisors
int countDivisors(int n) {
  // If number is 1, then it will have only 1
  // as a factor. So, total factors will be 1.
  if (n == 1)
    return 1;

  bool prime[n + 1], primesquare[n * n + 1];

  int a[n]; // for storing primes upto n

  // Calling SieveOfEratosthenes to store prime
  // factors of n and to store square of prime
  // factors of n
  SieveOfEratosthenes(n, prime, primesquare, a);

  // ans will contain total number of distinct
  // divisors
  int ans = 1;

  // Loop for counting factors of n
  for (int i = 0;; i++) {
    // a[i] is not less than cube root n
    if (a[i] * a[i] * a[i] > n)
      break;

    // Calculating power of a[i] in n.
    int cnt = 1;          // cnt is power of prime a[i] in n.
    while (n % a[i] == 0) // if a[i] is a factor of n
    {
      n = n / a[i];
      cnt = cnt + 1; // incrementing power
    }

    // Calculating number of divisors
    // If n = a^p * b^q then total divisors of n
    // are (p+1)*(q+1)
    ans = ans * cnt;
  }

  // if a[i] is greater than cube root of n

  // First case
  if (prime[n])
    ans = ans * 2;

  // Second case
  else if (primesquare[n])
    ans = ans * 3;

  // Third casse
  else if (n != 1)
    ans = ans * 4;

  return ans; // Total divisors
}
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);

  int t = 1;
  // cin>>t;
  while (t--) {

    int ans = 0;
    int n;
    cin >> n;

    for (int i = 1; i <= n; i++) {
      ans += countDivisors(i) * i;
    }
    cout << ans;
  }
}