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  1. #include <iostream>
  2. #include <cmath>
  3. #include <chrono>
  4. #include <iomanip>
  5. #include <sstream>
  6. #include <string>
  7.  
  8. #define endl '\n'
  9.  
  10. bool is_prime(unsigned n) {
  11.     if(n == 2 || n == 3) return true;
  12.     if(n % 2 == 0 || n % 3 == 0) return false;
  13.  
  14.     unsigned i=5, w=2;
  15.  
  16.     while(i*i <= sqrt(n)) {
  17.         if(n%i == 0) return false;
  18.  
  19.         i += w;
  20.         w = 6-w;
  21.     }
  22.     return true;
  23. }
  24.  
  25. std::string ftos(float f, int precision = 5) {
  26.     std::stringstream ss;
  27.     ss << std::fixed << std::setprecision(precision) << f;
  28.     return ss.str();
  29. }
  30.  
  31. int main() {
  32.  
  33.     unsigned max = 10000000, counters_found = 0;
  34.     bool flag = false;
  35.  
  36.     auto start = std::chrono::high_resolution_clock::now();
  37.  
  38.     // iterate thru odd numbers n
  39.     for(unsigned i=3; i <= max; i += 2){
  40.  
  41.         for(unsigned j=1; j<i; j++) {
  42.             if(is_prime(j*j + (i-j)*(i-j))) {
  43.                 flag = true;
  44.                 //std::cout << j << "^2 + " << (i-j) << "^2 is prime (" << i << ")" << endl;
  45.                 break;
  46.             }
  47.         }
  48.         if(!flag) {
  49.             std::cout << "counter: " << i << endl;
  50.             ++counters_found;
  51.         }
  52.         flag = false;
  53.     }
  54.  
  55.     auto end = std::chrono::high_resolution_clock::now();
  56.     auto duration = std::chrono::duration_cast<std::chrono::duration<double>>(end-start);
  57.     std::cout << counters_found
  58.               << " counter(s) found for n <= "
  59.               << max
  60.               << ". \nSearch took "
  61.               << ftos(duration.count(), 5)
  62.               << " second(s) and approximately "
  63.               << ftos(duration.count() / max, 10)
  64.               << " second(s) per integer."
  65.               << endl;
  66.  
  67.     return 0;
  68. }
Success #stdin #stdout 1.63s 15240KB
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Standard input is empty
stdout
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0 counter(s) found for n <= 10000000. 
Search took 1.63438 second(s) and approximately 0.0000001634 second(s) per integer.
https://ideone.com/k143ha
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
public

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