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  1. import java.util.ArrayList;
  2. import java.util.Collections;
  3. import java.util.List;
  4. import java.util.Random;
  5. import java.util.stream.Collectors;
  6.  
  7. class MontyHallProblem
  8. {
  9. 	static final int DOORS_SIZE = 3;
  10. 	static final int REPETITIONS_NUMBER = 1000;
  11. 	static final Random random;
  12. 	static
  13. 	{
  14. 		random = new Random();
  15. 	}
  16. 	static class Door
  17. 	{
  18. 		boolean car;
  19. 		boolean firstChoiced;
  20. 		boolean opened;
  21. 		Door(boolean car)
  22. 		{
  23. 			this.car = car;
  24. 			firstChoiced = false;
  25. 			opened = false;
  26. 		}
  27. 	}
  28. 	static abstract class Player
  29. 	{
  30. 		int firstWonsNumber;
  31. 		int secondWonsNumber;
  32. 		Player()
  33. 		{
  34. 			firstWonsNumber = 0;
  35. 			secondWonsNumber = 0;
  36. 		}
  37. 		Door firstChoice(List<Door> doors)
  38. 		{
  39. 			final Door door = randomChoice(doors);
  40. 			door.firstChoiced = true;
  41. 			return door;
  42. 		}
  43. 		abstract Door secondChoice(List<Door> doors);
  44. 	}
  45. 	static class ImmutablePlayer extends Player
  46. 	{
  47. 		Door secondChoice(List<Door> doors)
  48. 		{
  49. 			return doors.stream()
  50. 					.filter(door -> door.firstChoiced)
  51. 					.findFirst()
  52. 					.get();
  53. 		}
  54. 	}
  55. 	static class MutablePlayer extends Player
  56. 	{
  57. 		Door secondChoice(List<Door> doors)
  58. 		{
  59. 			return randomChoice(doors.stream()
  60. 					.filter(door -> !door.opened)
  61. 					.collect(Collectors.toList()));
  62. 		}
  63. 	}
  64. 	static class Game
  65. 	{
  66. 		List<Door> doors;
  67. 		Game()
  68. 		{
  69. 			doors = new ArrayList();
  70. 			doors.add(new Door(true));
  71. 			while (doors.size() < DOORS_SIZE) doors.add(new Door(false));
  72. 			Collections.shuffle(doors);
  73. 		}
  74. 		void openAnother()
  75. 		{
  76. 			randomChoice(doors.stream()
  77. 					.filter(door -> !door.car && !door.firstChoiced)
  78. 					.collect(Collectors.toList())).opened = true;
  79. 		}
  80. 		void play(Player player)
  81. 		{
  82. 			if (player.firstChoice(doors).car) ++player.firstWonsNumber;
  83. 			openAnother();
  84. 			if (player.secondChoice(doors).car) ++player.secondWonsNumber;
  85. 		}
  86. 	}
  87. 	public static void main(String[] args)
  88. 	{
  89. 		final Player immutablePlayer = new ImmutablePlayer();
  90. 		repeat(immutablePlayer);
  91. 		System.out.printf
  92. 		(
  93. 			"Immutable first=%d second=%d\n", 
  94. 			immutablePlayer.firstWonsNumber,
  95. 			immutablePlayer.secondWonsNumber
  96. 		);
  97. 		final Player mutablePlayer = new MutablePlayer();
  98. 		repeat(mutablePlayer);
  99. 		System.out.printf
  100. 		(
  101. 			"Mutable first=%d second=%d\n",
  102. 			mutablePlayer.firstWonsNumber,
  103. 			mutablePlayer.secondWonsNumber
  104. 		);
  105. 	}
  106. 	static <T> T randomChoice(List<T> list)
  107. 	{
  108. 		return list.get(random.nextInt(list.size()));
  109. 	}
  110. 	static void repeat(Player player)
  111. 	{
  112. 		for (int i = 0; i < REPETITIONS_NUMBER; ++i) new Game().play(player);
  113. 	}
  114. }
Success #stdin #stdout 0.13s 37336KB
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Standard input is empty
stdout
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Immutable first=353 second=353
Mutable first=361 second=456
https://ideone.com/Nr92SS
language:
Java (HotSpot 12)
created:
4 years ago
visibility:
public

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