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  1. // Divisor Summotary Function
  2. #pragma GCC optimize("Ofast")
  3. #include <bits/stdc++.h>
  4. using namespace std;
  5. using ll = long long;
  6. #define int long long
  7.  
  8. ll sum(ll l, ll r)
  9. {
  10.     return r * (r + 1) / 2 - l * (l + 1) / 2 + l;
  11. }
  12. ll const N = 9;
  13. void Solve()
  14. {
  15.     ll divSum = 0;
  16.     for (int i = 1; i * i <= N; i++) {
  17.         // value <= sqrt(N)
  18.         ll multiplier = N / i;
  19.         divSum += i * multiplier;
  20.         // value > sqrt(N)
  21.         ll NbyA = i; // count
  22.  
  23.         ll highestVal = N / i;
  24.         ll lowestVal = N / (i + 1) + 1;
  25.  
  26.         lowestVal = max(lowestVal, i + 1); // FIX: Value must be greater than sqrtN or i
  27.         if (lowestVal <= highestVal) // FIX: Removes duplicate addition in square number
  28.         	divSum += NbyA * sum(lowestVal, highestVal); // count * sum of values in range
  29.     }
  30.     cout << divSum << '\n';
  31. }
  32.  
  33. int32_t main()
  34. {
  35.     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  36.     int t = 1;
  37.     // cin >> t;
  38.     for (int i = 1; i <= t; i++) {
  39.         Solve();
  40.     }
  41.     return 0;
  42. }
  43. // Coded by Tahsin Arafat (@TahsinArafat)
  44.  
Success #stdin #stdout 0s 5316KB
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https://ideone.com/CxaICH
language:
C++14 (gcc 8.3)
created:
1 hour ago
visibility:
public

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