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

/*------------------------------------------HARSH_JIIT------------------------------------------------*/

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
/*----------------------------------------------------------------------------------------------------*/
#define int long long
#define mkp make_pair
#define pb push_back
#define ff first
#define ss second
#define Endl endl
#define rep(i, n) for (int i = 0; i < n; i++)
#define repr(i, a, b) for (int i = a; i < b; i++)
#define repre(i, a, b) for (int i = a; i <= b; i++)
#define dep(i, n) for (int i = n; i >= 0; i--)
#define depr(i, n, d) for (int i = n; i > d; i--)
#define depre(i, n, d) for (int i = n; i >= d; i--)
#define pi pair<int, int>
#define pii pair<int, pi>
#define mp map<int, int>
#define ump unordered_map<int, int>
#define st set<int>
#define ust unordered_set<int>
#define mst multiset<int>
#define pq priority_queue
#define mpq priority_queue<int, vector<int>, greater<int>>
#define allv(vec) vec.begin(), vec.end()
#define alla(arr, n) arr, arr + n
#define iofile                                                                 \\
  freopen("input.txt", "r", stdin);                                            \\
  freopen("output.txt", "w", stdout);
#define fastio                                                                 \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
#define tcase                                                                  \\
  int test_case;                                                               \\
  cin >> test_case;                                                            \\
  while (test_case--)
#define out(vec)                                                               \\
  for (auto it : vec) {                                                        \\
    cout << it << " ";                                                         \\
  }                                                                            \\
  cout << Endl;
typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedMSet;
//*p.find_by_order(index) return value at index
// p.order_of_key(key) return index
/*----------------------------------------------------------------------------------------------------*/
bool isPrime(int n);
int pow(int a, int b);
int gcd(int a, int b);
int modinv(int a, int m);
int pow(int a, int b, int mod);
int gcdExtended(int a, int b, int *x, int *y);
/*----------------------------------------------------------------------------------------------------*/
#define MAXN 100005
#define MOD 1000000007
/*---------------------------------------------MAIN---------------------------------------------------*/

int32_t main() {
  fastio
  // tcase
  {
    int n, ans = 0;
    cin >> n;
    repre(i, 1, n) {
      for (int j = i; j <= n; j += i)
        ans += j;
    }
    cout << ans << endl;
  }
  return 0;
}

/*--------------------------------------END OF MAIN
 * FUNCTION------------------------------------------*/
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int gcdExtended(int a, int b, int *x, int *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  int x1, y1;
  int gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int modinv(int a, int m) {
  int x, y;
  int g = gcdExtended(a, m, &x, &y);
  int res = (x % m + m) % m;
  return res;
}
bool isPrime(int n) {
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;
  if (n % 2 == 0 || n % 3 == 0)
    return false;
  int p = sqrt(n);
  for (int i = 5; i <= p; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;
  return true;
}
int pow(int a, int b) {
  int res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
int pow(int a, int b, int mod) {
  a %= mod;
  int res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res;
}


Error: TLE

Fixed submission:

/*------------------------------------------HARSH_JIIT------------------------------------------------*/

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
/*----------------------------------------------------------------------------------------------------*/
#define int long long
#define mkp make_pair
#define pb push_back
#define ff first
#define ss second
#define Endl endl
#define rep(i, n) for (int i = 0; i < n; i++)
#define repr(i, a, b) for (int i = a; i < b; i++)
#define repre(i, a, b) for (int i = a; i <= b; i++)
#define dep(i, n) for (int i = n; i >= 0; i--)
#define depr(i, n, d) for (int i = n; i > d; i--)
#define depre(i, n, d) for (int i = n; i >= d; i--)
#define pi pair<int, int>
#define pii pair<int, pi>
#define mp map<int, int>
#define ump unordered_map<int, int>
#define st set<int>
#define ust unordered_set<int>
#define mst multiset<int>
#define pq priority_queue
#define mpq priority_queue<int, vector<int>, greater<int>>
#define allv(vec) vec.begin(), vec.end()
#define alla(arr, n) arr, arr + n
#define iofile                                                                 \\
  freopen("input.txt", "r", stdin);                                            \\
  freopen("output.txt", "w", stdout);
#define fastio                                                                 \\
  ios_base::sync_with_stdio(false);                                            \\
  cin.tie(NULL);                                                               \\
  cout.tie(NULL);
#define tcase                                                                  \\
  int test_case;                                                               \\
  cin >> test_case;                                                            \\
  while (test_case--)
#define out(vec)                                                               \\
  for (auto it : vec) {                                                        \\
    cout << it << " ";                                                         \\
  }                                                                            \\
  cout << Endl;
typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedMSet;
//*p.find_by_order(index) return value at index
// p.order_of_key(key) return index
/*----------------------------------------------------------------------------------------------------*/
bool isPrime(int n);
int pow(int a, int b);
int gcd(int a, int b);
int modinv(int a, int m);
int pow(int a, int b, int mod);
int gcdExtended(int a, int b, int *x, int *y);
/*----------------------------------------------------------------------------------------------------*/
#define MAXN 100005
#define MOD 1000000007
/*---------------------------------------------MAIN---------------------------------------------------*/
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() {
  fastio
  // tcase
  {
    int ans = 0;
    int n;
    cin >> n;
    repre(i, 1, n) ans += i * countDivisors(i);
    cout << ans;
  }
  return 0;
}

/*--------------------------------------END OF MAIN
 * FUNCTION------------------------------------------*/
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int gcdExtended(int a, int b, int *x, int *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  int x1, y1;
  int gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int modinv(int a, int m) {
  int x, y;
  int g = gcdExtended(a, m, &x, &y);
  int res = (x % m + m) % m;
  return res;
}
bool isPrime(int n) {
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;
  if (n % 2 == 0 || n % 3 == 0)
    return false;
  int p = sqrt(n);
  for (int i = 5; i <= p; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;
  return true;
}
int pow(int a, int b) {
  int res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
int pow(int a, int b, int mod) {
  a %= mod;
  int res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res;
}