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  1. #include <iostream>
  2. #include <string>
  3. #include <array>
  4.  
  5. #define onlyAtEnd(a) typename std::enable_if<sizeof...(a) == 0 > ::type
  6.  
  7. template<int a, int b>
  8. class Entry
  9. {
  10. public:
  11. 	static constexpr int VAL = a;
  12. 	static constexpr int PROB = b;
  13. };
  14.  
  15. template<typename... EntryTypes>
  16. class NumChooser
  17. {
  18. private:
  19. 	const int SUM;
  20. 	static constexpr int NUM_VALS = sizeof...(EntryTypes);
  21.  
  22. public:
  23.  
  24. 	static constexpr int size()
  25. 	{
  26. 		return NUM_VALS;
  27. 	}
  28.  
  29. 	template<typename T, typename... args>
  30. 	constexpr int calcSum()
  31. 	{
  32. 		return T::PROB + calcSum < args...>();
  33. 	}
  34.  
  35. 	template <typename... Ts, typename = onlyAtEnd(Ts) >
  36. 	constexpr int calcSum()
  37. 	{
  38. 		return 0;
  39. 	}
  40.  
  41. 	NumChooser() : SUM(calcSum < EntryTypes... >()) { }
  42.  
  43. 	template<typename T, typename... args>
  44. 	constexpr int find(int left, int previous = 0)
  45. 	{
  46. 		return left < 0 ? previous : find < args... >(left - T::PROB, T::VAL);
  47. 	}
  48.  
  49. 	template <typename... Ts, typename = onlyAtEnd(Ts) >
  50. 	constexpr int find(int left, int previous)
  51. 	{
  52. 		return previous;
  53. 	}
  54.  
  55. 	constexpr int choose()
  56. 	{
  57. 		return find < EntryTypes... >(rand() % SUM);
  58. 	}
  59. };
  60.  
  61. NumChooser <
  62. Entry<0, 10>,
  63. Entry<1, 50>,
  64. Entry<2, 80>,
  65. Entry<3, 01>
  66. > chooser;
  67.  
  68. int main()
  69. {
  70. 	srand(time(nullptr));
  71. 	std::array<int, chooser.size() > frequency{};
  72. 	const int NUM_TRIALS = 10000;
  73. 	for (int i = 0; i < NUM_TRIALS; ++i)
  74. 	{
  75. 		int val = chooser.choose();
  76. 		frequency[val]++;
  77. 	}
  78. 	std::cout << "Frequency:" << std::endl;
  79. 	for (int i : frequency)
  80. 		std::cout << (float) i / NUM_TRIALS << " ";
  81. }
Success #stdin #stdout 0s 3412KB
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Standard input is empty
stdout
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Frequency:
0.0724 0.3571 0.5636 0.0069
https://ideone.com/sB0w45
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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