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

// Author- VMAX

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ordered_multiset                                                       \\
  tree<long long, null_type, less_equal<long long>, rb_tree_tag,               \\
       tree_order_statistics_node_update>
#define ordered_set                                                            \\
  tree<long long, null_type, less<long long>, rb_tree_tag,                     \\
       tree_order_statistics_node_update>
using namespace std;
#define ll long long int
#define YES                                                                    \\
  cout << "YES"                                                                \\
       << "\\n";
#define NO                                                                     \\
  cout << "NO"                                                                 \\
       << "\\n";
#define ld long double
#define yes                                                                    \\
  cout << "yes"                                                                \\
       << "\\n";
#define no                                                                     \\
  cout << "no"                                                                 \\
       << "\\n";
#define No                                                                     \\
  cout << "No"                                                                 \\
       << "\\n";
#define Yes                                                                    \\
  cout << "Yes"                                                                \\
       << "\\n";
#define f(i, a) for (i = 0; i < a; i++)
#define fo(i, a) for (i = 1; i <= a; i++)
#define fa(i, a) for (auto i : a)
#define r(i, a) for (auto i = a.rbegin(); i != a.rend(); i++)
#define en cout << "\\n";
#define ull unsigned long long int
#define o(x) cout << x << "\\n";
#define o1(x) cout << x << " ";
#define pb push_back
#define F first
#define in insert
#define mp make_pair
#define S second
#define pre(n) cout << fixed << setprecision(n);
#define gcd(a, b) __gcd(a, b)
#define bs binary_search
#define fast                                                                   \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);
#define test                                                                   \\
  ll t;                                                                        \\
  cin >> t;                                                                    \\
  while (t-- > 0)
const ll Mod = 998244353;
#define mod 1000000007
#define pi 3.14159265358979323846
#define all(x) x.begin(), x.end()
#define re return 0;
// *#######################################################################################*

/*
bool isp(ll n)
{
    ll i;
    for(i=2;i*i<=n;i++)
    {
        if(n%i==0)
        {
            return false;
        }

    }
}
  */
int main()

{

  fast ll n;
  cin >> n;
  ll j, i;
  vector<ll> a(n + 2, 1);
  for (i = 2; i <= n; i++) {
    for (j = i; j <= n; j += i) {
      a[j]++;
    }
  }

  ll s = 0;

  fo(i, n) {
    s += a[i] * i;
    // o1(a[i])
  }

  o(s)

      re
}

Error: TLE

Fixed submission:

// C++ program to count distinct divisors
// of a given number n
#include <bits/stdc++.h>
using namespace std;

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
}

// Driver Program
int main() {
  long long int n;
  cin >> n;
  long long int i, s = 0;

  for (i = 1; i <= n; i++) {
    s += i * countDivisors(i);
    // cout<<countDivisors(i);
  }

  cout << s << "\\n";
  return 0;
}