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  1. #include <iostream>
  2. #include <cmath>
  3. #include <unordered_set>
  4. #include <chrono>
  5.  
  6. struct EqualPred
  7. {
  8.     constexpr bool operator()(const double& lhs, const double& rhs) const
  9.     {
  10.         if (std::isnan(lhs) && std::isnan(rhs)) return true;
  11.         return lhs == rhs;
  12.     }
  13. };
  14.  
  15. template <typename T>
  16. struct Hash
  17. {
  18. 	size_t operator()(const T& value) const
  19. 	{
  20. 		return  std::hash<T>()( std::isnan(value) ? NAN : value);
  21. 	}
  22.  
  23.  
  24. };
  25.  
  26. std::unordered_set<double, Hash<double>, EqualPred> s;
  27.  
  28. constexpr int N=5000;
  29. void test_insert(double value)
  30. {
  31.  
  32.     auto begin = std::chrono::high_resolution_clock::now();
  33.     for (int i = 0; i < N; i++) {
  34.         s.insert(value);
  35.     }
  36.     auto end = std::chrono::high_resolution_clock::now();
  37.     std::cout << "Duration: " << (std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin).count() / 1e9) << "\n";
  38.     std::cout << "Number of elements: "<<s.size()<<"\n";
  39. }
  40.  
  41. int main(){
  42.     std::cout << "Not NAN\n";
  43.     test_insert(1.0);           //takes 0.0001 s
  44.     std::cout << "NAN\n";
  45.     test_insert(NAN);  
  46.     test_insert(-NAN);
  47.  
  48.     std::cout << s.size() << std::endl;
  49.     //takes 0.2 s
  50. }
Success #stdin #stdout 0s 4264KB
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stdin
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Standard input is empty
stdout
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Not NAN
Duration: 0.000180664
Number of elements: 1
NAN
Duration: 0.000192384
Number of elements: 2
Duration: 0.000154591
Number of elements: 2
2
https://ideone.com/pqk0ZC
language:
C++14 (gcc 8.3)
created:
5 years ago
visibility:
public

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