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

/// #pragma GCC optimize("O3,unroll-loops")
/// #pragma GCC target("avx,avx2,fma")

#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 ll long long
#define ull unsigned long long
#define ld long double
#define inf 2000000000
#define infLL 2000000000000000000
#define MAX5 100005
#define MAX6 1000006
#define MAX7 10000007
#define sf(a) scanf("%d", &a)
#define sfl(a) scanf("%lld", &a)
#define pf(a) printf("%d\\n", a)
#define pfl(a) printf("%lld\\n", a)
#define Case(t) printf("Case %d: ", t)
#define pii pair<int, int>
#define mod 1000000007
#define Mod 998244353
#define PI acos(-1.0)
#define eps 1e-9
#define mem(a, b) memset(a, b, sizeof(a))
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);

#define error(args...)                                                         \\
  {                                                                            \\
    string _s = #args;                                                         \\
    replace(_s.begin(), _s.end(), ',', ' ');                                   \\
    stringstream _ss(_s);                                                      \\
    istream_iterator<string> _it(_ss);                                         \\
    err(_it, args);                                                            \\
    cerr << '\\n';                                                              \\
  }

inline int Set(ll N, ll pos) { return N = N | (1LL << pos); }
inline int Reset(ll N, ll pos) { return N = N & ~(1LL << pos); }
inline bool Check(ll N, ll pos) { return (bool)(N & (1LL << pos)); }

inline bool Equal(ld x, ld y) { return fabs(x - y) < eps; } /// x==y
inline bool Greater(ld x, ld y) { return (x - eps) > y; }   /// x>y
inline bool Lesser(ld x, ld y) { return (x + eps) < y; }    /// x<y

inline void normal(ll &a) {
  a %= mod;
  (a < 0) && (a += mod);
}
inline ll modMul(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  return (a * b) % mod;
}
inline ll modAdd(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  return (a + b) % mod;
}
inline ll modSub(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  a -= b;
  normal(a);
  return a;
}
inline ll modPow(ll b, ll p) {
  ll r = 1;
  while (p) {
    if (p & 1LL)
      r = modMul(r, b);
    b = modMul(b, b);
    p >>= 1LL;
  }
  return r;
}
inline ll modInverse(ll a) { return modPow(a, mod - 2); }
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }

/// Memory Efficient
inline ll fast_exp(ll x, ll n, ll m) {
  ll res = 1;
  while (n > 0) {
    if (n % 2 == 1)
      res = (res * x) % m;
    x = (x * x) % m;
    n /= 2;
  }
  return res % m;
}

// int dx[] = {+0, +0, -1, +1}; ///Up-down, Left-Right
// int dy[] = {+1, -1, +0, +0};
// int dx[] = {+0,+0,+1,-1,-1,+1,-1,+1}; ///King's Move
// int dy[] = {-1,+1,+0,+0,+1,+1,-1,-1};
// int dx[] = {-2, -2, -1, -1,  1,  1,  2,  2}; ///Knight's Move
// int dy[] = {-1,  1, -2,  2, -2,  2, -1,  1};

void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << " ";
  err(++it, args...);
}

inline void Time() {
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\\n";
}

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet;
typedef tree<int, null_type, greater<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet1;

const int N = MAX7;
ll cnt[N];

int main() {
  // freopen("in.txt","r",stdin);
  // freopen("out.txt","w",stdout);

  FASTIO;
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j += i)
      cnt[j]++;
  ll ans = 0;
  for (ll i = 1; i <= n; i++)
    ans = ans + (cnt[i] * i);
  cout << ans << endl;

  Time();
  return 0;
}


Error: TLE

Fixed submission:

/// #pragma GCC optimize("O3,unroll-loops")
/// #pragma GCC target("avx,avx2,fma")

#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 ll long long
#define ull unsigned long long
#define ld long double
#define inf 2000000000
#define infLL 2000000000000000000
#define MAX5 100005
#define MAX6 1000006
#define MAX7 10000007
#define sf(a) scanf("%d", &a)
#define sfl(a) scanf("%lld", &a)
#define pf(a) printf("%d\\n", a)
#define pfl(a) printf("%lld\\n", a)
#define Case(t) printf("Case %d: ", t)
#define pii pair<int, int>
#define mod 1000000007
#define Mod 998244353
#define PI acos(-1.0)
#define eps 1e-9
#define mem(a, b) memset(a, b, sizeof(a))
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);

#define error(args...)                                                         \\
  {                                                                            \\
    string _s = #args;                                                         \\
    replace(_s.begin(), _s.end(), ',', ' ');                                   \\
    stringstream _ss(_s);                                                      \\
    istream_iterator<string> _it(_ss);                                         \\
    err(_it, args);                                                            \\
    cerr << '\\n';                                                              \\
  }

inline int Set(ll N, ll pos) { return N = N | (1LL << pos); }
inline int Reset(ll N, ll pos) { return N = N & ~(1LL << pos); }
inline bool Check(ll N, ll pos) { return (bool)(N & (1LL << pos)); }

inline bool Equal(ld x, ld y) { return fabs(x - y) < eps; } /// x==y
inline bool Greater(ld x, ld y) { return (x - eps) > y; }   /// x>y
inline bool Lesser(ld x, ld y) { return (x + eps) < y; }    /// x<y

inline void normal(ll &a) {
  a %= mod;
  (a < 0) && (a += mod);
}
inline ll modMul(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  return (a * b) % mod;
}
inline ll modAdd(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  return (a + b) % mod;
}
inline ll modSub(ll a, ll b) {
  a %= mod, b %= mod;
  normal(a), normal(b);
  a -= b;
  normal(a);
  return a;
}
inline ll modPow(ll b, ll p) {
  ll r = 1;
  while (p) {
    if (p & 1LL)
      r = modMul(r, b);
    b = modMul(b, b);
    p >>= 1LL;
  }
  return r;
}
inline ll modInverse(ll a) { return modPow(a, mod - 2); }
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }

/// Memory Efficient
inline ll fast_exp(ll x, ll n, ll m) {
  ll res = 1;
  while (n > 0) {
    if (n % 2 == 1)
      res = (res * x) % m;
    x = (x * x) % m;
    n /= 2;
  }
  return res % m;
}

// int dx[] = {+0, +0, -1, +1}; ///Up-down, Left-Right
// int dy[] = {+1, -1, +0, +0};
// int dx[] = {+0,+0,+1,-1,-1,+1,-1,+1}; ///King's Move
// int dy[] = {-1,+1,+0,+0,+1,+1,-1,-1};
// int dx[] = {-2, -2, -1, -1,  1,  1,  2,  2}; ///Knight's Move
// int dy[] = {-1,  1, -2,  2, -2,  2, -1,  1};

void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << " ";
  err(++it, args...);
}

inline void Time() {
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\\n";
}

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet;
typedef tree<int, null_type, greater<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    orderedSet1;

const int N = MAX7;

bool prime[N];
vector<int> p;

void sieve() {
  memset(prime, 0, sizeof(prime));
  prime[0] = prime[1] = 1;

  for (int i = 4; i < N; i += 2) {
    prime[i] = 1;
  }
  for (int i = 3; i * i < N; i += 2) {
    if (!prime[i]) {
      for (int j = i * i; j < N; j += i)
        prime[j] = 1; /// not prime
    }
  }

  for (int i = 2; i < N; i++)
    if (!prime[i])
      p.push_back(i);
}

ll NOD(int n) {
  int sqrtn = sqrt(n);
  ll res = 1;
  for (int i = 0; i < p.size() && p[i] <= sqrtn; i++) {
    if (n % p[i] == 0) {
      int tot = 0;
      while (n % p[i] == 0) {
        n /= p[i];
        tot++;
      }
      sqrtn = sqrt(n);
      tot++;
      res *= (ll)tot;
    }
  }
  if (n != 1)
    res *= 2LL;
  return res;
}

int main() {
  // freopen("in.txt","r",stdin);
  // freopen("out.txt","w",stdout);

  FASTIO;
  sieve();
  int n;
  sf(n);
  ll ans = 0;
  for (int i = 1; i <= n; i++) {
    ll num = NOD(i);
    ans = ans + ((ll)i * num);
  }
  pfl(ans);

  Time();
  return 0;
}