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  1. #include <cmath>
  2. #include <iostream>
  3. #include <vector>
  4. #include <stdint.h>
  5.  
  6. namespace {
  7.   // yield all prime numbers less than limit.
  8.   // http://r...content-available-to-author-only...e.org/wiki/Category:C%2B%2B
  9.   template<class UnaryFunction>
  10.   void primesupto(int limit, UnaryFunction yield)
  11.   {
  12.     std::vector<bool> is_prime(limit, true);
  13.  
  14.     const int sqrt_limit = static_cast<int>(std::sqrt(limit));
  15.     for (int n = 2; n <= sqrt_limit; ++n)
  16.       if (is_prime[n]) {
  17. 	yield(n);
  18.  
  19. 	for (unsigned k = n*n, ulim = static_cast<unsigned>(limit); k < ulim; k += n)
  20. 	  //NOTE: "unsigned" is used to avoid an overflow in `k+=n` for `limit` near INT_MAX
  21. 	  is_prime[k] = false;
  22.       }
  23.  
  24.     for (int n = sqrt_limit + 1; n < limit; ++n)
  25.       if (is_prime[n])
  26. 	yield(n);
  27.   }
  28. }
  29.  
  30. int main() {
  31.   uintmax_t sum = 0;
  32.   primesupto(2000000, [&sum] (int prime) { sum += prime; });
  33.   std::cout << sum << std::endl;
  34. }
  35.  
Success #stdin #stdout 0.01s 2828KB
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142913828922
https://ideone.com/OW197
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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