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  1. #include <utility>
  2. #include <vector>
  3.  
  4. std::vector< std::pair<int, int> > factor_table;
  5. void fill_sieve( int n )
  6. {
  7.     factor_table.resize(n+1);
  8.     for( int i = 1; i <= n; ++i ) {
  9.         if (i & 1)
  10.             factor_table[i] = std::pair<int, int>(i, 1);
  11.         else
  12.             factor_table[i] = std::pair<int, int>(2, i>>1);
  13.     }
  14.     for( int j = 3, j2 = 9; j2 <= n; ) {
  15.         if (factor_table[j].second == 1) {
  16.             int i = j;
  17.             int ij = j2;
  18.             while (ij <= n) {
  19.                 factor_table[ij] = std::pair<int, int>(j, i);
  20.                 ++i;
  21.                 ij += j;
  22.             }
  23.         }
  24.         j2 += (j + 1) << 2;
  25.         j += 2;
  26.     }
  27. }
  28.  
  29. std::vector<int> factor( int num )
  30. {
  31.     std::vector<int> factors;
  32.     factors.reserve(30);
  33.     do {
  34.         factors.push_back(factor_table[num].first);
  35.         num = factor_table[num].second;
  36.     } while (num != 1);
  37.     return factors;
  38. }
  39.  
  40. const unsigned MAX = 10000000;
  41.  
  42. int main()
  43. {
  44.     fill_sieve(MAX);
  45.  
  46.     std::vector<int> factors;
  47.     for (int k = 1; k < MAX; k++) {
  48.         factor(k).swap(factors);
  49.     }
  50. }
Success #stdin #stdout 2.32s 2960KB
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https://ideone.com/pt9nu
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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