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  1. #include <iostream>
  2. #include <string>
  3. #include <array>
  4. #include <random>
  5.  
  6. #define onlyAtEnd(a) typename std::enable_if<sizeof...(a) == 0 > ::type
  7.  
  8. template<int a, int b>
  9. class Entry
  10. {
  11. public:
  12. 	static constexpr int VAL = a;
  13. 	static constexpr int PROB = b;
  14. };
  15.  
  16. template<typename... EntryTypes>
  17. class NumChooser
  18. {
  19. private:
  20. 	const int SUM;
  21. 	static constexpr int NUM_VALS = sizeof...(EntryTypes);
  22. 	std::mt19937 gen;
  23. 	std::uniform_int_distribution<> dist;
  24.  
  25. public:
  26.  
  27. 	static constexpr int size()
  28. 	{
  29. 		return NUM_VALS;
  30. 	}
  31.  
  32. 	template<typename T, typename... args>
  33. 	constexpr int calcSum()
  34. 	{
  35. 		return T::PROB + calcSum < args...>();
  36. 	}
  37.  
  38. 	template <typename... Ts, typename = onlyAtEnd(Ts) >
  39. 	constexpr int calcSum()
  40. 	{
  41. 		return 0;
  42. 	}
  43.  
  44. 	NumChooser() : SUM(calcSum < EntryTypes... >()), gen(std::random_device{}()), dist(1, SUM) { }
  45.  
  46. 	template<typename T, typename... args>
  47. 	constexpr int find(int left, int previous = 0)
  48. 	{
  49. 		return left < 0 ? previous : find < args... >(left - T::PROB, T::VAL);
  50. 	}
  51.  
  52. 	template <typename... Ts, typename = onlyAtEnd(Ts) >
  53. 	constexpr int find(int left, int previous)
  54. 	{
  55. 		return previous;
  56. 	}
  57.  
  58. 	int choose()
  59. 	{
  60. 		return find < EntryTypes... >(dist(gen));
  61. 	}
  62. };
  63.  
  64. NumChooser <
  65. Entry<0, 10>,
  66. Entry<1, 50>,
  67. Entry<2, 80>,
  68. Entry<3, 01>
  69. > chooser;
  70.  
  71. int main()
  72. {
  73. 	std::array<int, chooser.size() > frequency{};
  74. 	const int NUM_TRIALS = 10000;
  75. 	for (int i = 0; i < NUM_TRIALS; ++i)
  76. 	{
  77. 		int val = chooser.choose();
  78. 		frequency[val]++;
  79. 	}
  80. 	std::cout << "Frequency:" << std::endl;
  81. 	for (int i : frequency)
  82. 		std::cout << (float) i / NUM_TRIALS << " ";
  83. }
Success #stdin #stdout 0s 3464KB
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Standard input is empty
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Frequency:
0.0656 0.3522 0.5659 0.0163
https://ideone.com/0sT3dT
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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