Problem p02624 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define pb push_back
#define vi vector<int>
#define pob push_back
#define pf pop_front()
#define mp make_pair
#define loop(i, a, b) for (int i = a; i < b; ++i)
#define eloop(i, a, b) for (int i = a; i <= b; ++i)
#define rloop(i, a, b) for (int i = b - 1; i >= b; --i)
#define MAP map<int, int>
#define DQ deque<int>
#define vf(i) v[i].first
#define vs(i) v[i].second
#define mod 1000000007
#define M 998244353
#define faster                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL)
int binarySearch(int arr[], int l, int r, int x) {
  if (r >= l) {
    int mid = l + (r - l) / 2;

    // If the element is present at the middle
    // itself
    if (arr[mid] == x)
      return mid;

    // If element is smaller than mid, then
    // it can only be present in left subarray
    if (arr[mid] > x)
      return binarySearch(arr, l, mid - 1, x);

    // Else the element can only be present
    // in right subarray
    return binarySearch(arr, mid + 1, r, x);
  }

  // We reach here when element is not
  // present in array
  return -1;
}

bool isPrime(int n) {
  // Corner cases
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;

  // This is checked so that we can skip
  // middle five numbers in below loop
  if (n % 2 == 0 || n % 3 == 0)
    return false;

  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;

  return true;
}

bool isPowerOfTwo(int x) {
  /* First x in the below expression is for the case when x is 0 */
  return x && (!(x & (x - 1)));
}

int countBits(int number) {
  // log function in base 2
  // take only integer part
  return (int)log2(number) + 1;
}

int countSetBits(int n) {
  int count = 0;
  while (n) {
    count += n & 1;
    n >>= 1;
  }
  return count;
}

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() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  int n, s = 0;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    s = s + (i * countDivisors(i));
  }
  cout << s << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define pb push_back
#define vi vector<int>
#define pob push_back
#define pf pop_front()
#define mp make_pair
#define loop(i, a, b) for (int i = a; i < b; ++i)
#define eloop(i, a, b) for (int i = a; i <= b; ++i)
#define rloop(i, a, b) for (int i = b - 1; i >= b; --i)
#define MAP map<int, int>
#define DQ deque<int>
#define vf(i) v[i].first
#define vs(i) v[i].second
#define mod 1000000007
#define M 998244353
#define faster                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL)
int binarySearch(int arr[], int l, int r, int x) {
  if (r >= l) {
    int mid = l + (r - l) / 2;

    // If the element is present at the middle
    // itself
    if (arr[mid] == x)
      return mid;

    // If element is smaller than mid, then
    // it can only be present in left subarray
    if (arr[mid] > x)
      return binarySearch(arr, l, mid - 1, x);

    // Else the element can only be present
    // in right subarray
    return binarySearch(arr, mid + 1, r, x);
  }

  // We reach here when element is not
  // present in array
  return -1;
}

bool isPrime(int n) {
  // Corner cases
  if (n <= 1)
    return false;
  if (n <= 3)
    return true;

  // This is checked so that we can skip
  // middle five numbers in below loop
  if (n % 2 == 0 || n % 3 == 0)
    return false;

  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0)
      return false;

  return true;
}

bool isPowerOfTwo(int x) {
  /* First x in the below expression is for the case when x is 0 */
  return x && (!(x & (x - 1)));
}

int countBits(int number) {
  // log function in base 2
  // take only integer part
  return (int)log2(number) + 1;
}

int countSetBits(int n) {
  int count = 0;
  while (n) {
    count += n & 1;
    n >>= 1;
  }
  return count;
}

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() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif
  int n, s = 0;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    int y = n / i;
    int ans = (y * (y + 1) * i) / 2;
    s += ans;
  }
  cout << s << endl;

  return 0;
}