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

#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define ini(arr, val) memset(arr, (val), sizeof(arr))
#define loop(i, n) for (ll i = 0; i < n; i++)
#define loop1(i, n) for (ll i = 1; i <= n; i++)

#define all(a) (a).begin(), (a).end()
#define dupli(a) unique(all(a)), (a).end()
#define exist(s, e) (s.find(e) != s.end())
#define dbg(x) cout << #x << " is " << x << endl;
#define pt(x) cout << x << "\\n"
#define pts(x) cout << x << " "

#define mp make_pair
#define pb push_back
#define f first
#define s second

#define inf (int)1e9
#define eps 1e-9
#define PI 3.1415926535897932384626433832795
#define mod 1000000007

#define fast                                                                   \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define test                                                                   \\
  int t;                                                                       \\
  cin >> t;                                                                    \\
  while (t--)

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector<vi> vvi;
typedef map<int, int> mii;
typedef set<int> si;

typedef pair<ll, ll> pll;
typedef vector<ll> vl;
typedef vector<string> vs;
typedef vector<pll> vpll;
typedef vector<vl> vvl;
typedef map<ll, ll> mll;
typedef set<ll> sl;

//////////////////////////////////////////////////////////////////////////////////////////
//                      main starts
//////////////////////////////////////////////////////////////////////////////////////////
int const lmt = 1e7 + 5;
int min_prime[lmt];

void seive() {
  loop(i, lmt) min_prime[i] = i;

  for (int ll i = 2; i < lmt; i++) {
    if (min_prime[i] == i) {
      for (ll j = i * i; j < lmt; j += i)
        min_prime[j] = i;
    }
  }
}

ll count(ll n) {
  // return 0;
  ll ans = 1;
  while (n > 1) {
    ll mp = min_prime[n];
    int cnt = 1;
    while (n % mp == 0) {
      n /= mp;
      cnt++;
    }
    ans = (cnt * ans);
  }
  return ans;
}

int main() {

  //    #ifndef ONLINE_JUDGE
  //    freopen("../input.txt", "r", stdin);
  //    freopen("../output.txt", "w", stdout);
  // #endif
  fast

  // pt("jdbshfjk");
  seive();

  ll n;
  cin >> n;

  ll sum = 0;
  loop1(i, n) { sum += i * count(i); }

  pt(sum);
}

/*

//

*/

Error: TLE

Fixed submission:

#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define ini(arr, val) memset(arr, (val), sizeof(arr))
#define loop(i, n) for (ll i = 0; i < n; i++)
#define loop1(i, n) for (ll i = 1; i <= n; i++)

#define all(a) (a).begin(), (a).end()
#define dupli(a) unique(all(a)), (a).end()
#define exist(s, e) (s.find(e) != s.end())
#define dbg(x) cout << #x << " is " << x << endl;
#define pt(x) cout << x << "\\n"
#define pts(x) cout << x << " "

#define mp make_pair
#define pb push_back
#define f first
#define s second

#define inf (int)1e9
#define eps 1e-9
#define PI 3.1415926535897932384626433832795
#define mod 1000000007

#define fast                                                                   \\
  ios_base::sync_with_stdio(0);                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);
#define test                                                                   \\
  int t;                                                                       \\
  cin >> t;                                                                    \\
  while (t--)

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector<vi> vvi;
typedef map<int, int> mii;
typedef set<int> si;

typedef pair<ll, ll> pll;
typedef vector<ll> vl;
typedef vector<string> vs;
typedef vector<pll> vpll;
typedef vector<vl> vvl;
typedef map<ll, ll> mll;
typedef set<ll> sl;

//////////////////////////////////////////////////////////////////////////////////////////
//                      main starts
//////////////////////////////////////////////////////////////////////////////////////////
int const lmt = 1e5 + 5;
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++;
    }
  }
}
int count(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
}

int main() {

  ll n;
  cin >> n;
  ll sum = 0;
  loop1(i, n) { sum += i * count(i); }

  pt(sum);
}

/*

//

*/