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Monty Hall Simulator for 3 items

Byers Dec 23rd, 2011 160 Never
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  1. /**
  2. * Monty Hall Simulator
  3. * Shows the probabilty of getting the price if you do not change your choice or if you do
  4. * The Program starts with a random "door" array, with two fails (0's) and one price (1)
  5. * The "user" choices random position, then the program deletes one fail (turning it into -1)
  6. * and the user changes his choice (successIfChange) and test whether he gets the price or not
  7. * same test is done simultaneosly choicing not to change his choice ()
  8. * then the success rate for both cases are shown for a  big amount of tries
  9. * For customizing the numbr of tries, edit the NUMBER_OF_TRIES constant
  10. * @author E.A [agua15@eresmas.com]
  11. */
  12.  
  13. int NUMBER_OF_TRIES=1000000;
  14.  
  15. /**
  16. * Returns a random array of 3 positions with two fails(0's) and one price (1)
  17. */
  18. int[] fillArray()
  19. {
  20. int[] myarray=new int[3];
  21. int candidate= (int) ((Math.random ()*100) % 3);
  22. myarray[candidate]=1;
  23. for (int i=0;i<3;i++){
  24.   if(myarray[i]!=1) myarray[i]=0;
  25. }
  26. return myarray;
  27. }
  28.  
  29. /**
  30. * Gets the position of the price ('1' value) for the current array
  31. */
  32. int getPricePosition(int[] array)
  33. {
  34. for (int i=0;i<3;i++){
  35.   if (array[i]==1) return i;
  36. }
  37. return -1;
  38. }
  39.  
  40. /**
  41. * Change user choice amongst the another unique valid choice
  42. * @param guess user original guess
  43. * @discarded forbidden choice as it was "revealed" by the program
  44. * @myarray array with one price(1), one fail(0), and one discarded item (-1)
  45. */
  46. int changePos(int guess,int discarded,int[] myarray)
  47. {
  48. for (int i=0;i<3;i++){
  49.   if (i!=guess && i!=discarded) return i;
  50. }
  51. return -1;
  52. }
  53.  
  54. /**
  55. *  Trim door array with two valid positions,
  56. *  one must be the price
  57. *  and return the position of the discarded door
  58. *  @param myarray original door array
  59. *  @param myguess user guess of price
  60. *  @one real position of price
  61. */
  62. int getChoicedArray(int[] myarray,int myGuess,int one){
  63.   int[] small= new int[3];
  64.   boolean flag=true;
  65.  for (int k=0;k<3;k++){
  66.    small[k]=0; //default fill
  67.   if (k==one) { // compulsory item, must not be discared
  68.      small[k]=myarray[k]; //will be 1 ,otherwise algorithm is wrong
  69.      if (small[k]!=1) return -1;// error, should never happen
  70.    }else if(flag && k!=myGuess){ //discarded option
  71.      small[k]=-1;
  72.      flag=false; // do not enter this condition again
  73.    }
  74.  
  75.   }
  76.   // return position of discarded door
  77.  for  (int i=0;i<3;i++){
  78.    if (small[i]==-1)return i;  
  79.  }
  80.  return -1; // error, should never happen
  81. }
  82.  
  83. /**
  84. *  Main flow of the program:
  85. *  get the original door array . Example: [0,1,0] two fails and one price
  86. *  get user's choice: (possible values: 0,1,2). For Example: 1
  87. *  Discard a fail : Example: [-1,1,0]
  88. *  Change user's mind: Choice position 2 (NO SUCCESS)
  89. *  If user does not change his mind: Position 1 (SUCCESS)
  90. *  Register this success rate for NUMBER_OF_TRIES times
  91. *
  92. */
  93. int successIfNotChange=0;
  94. int successIfChange=0;
  95. for (int i=0;i <NUMBER_OF_TRIES; i++){
  96.  def myarray =fillArray(); //get original door array
  97.  int one=getPricePosition(myarray); //get position of the price (1)
  98.  int myGuess= (int) ((Math.random ()*100) % 3); //user choices a position
  99.   //trim door array with two remaining positions, and get the position of the discarded door
  100.  int discarded=getChoicedArray(myarray,myGuess,one);  
  101.  if(myarray[myGuess]==1){ //keep original  user choice and see if user was right
  102.     successIfNotChange++;
  103.   }
  104.   //ExChange  user choice  with the alternative remaining door and see if success
  105.  if (myarray[changePos(myGuess,discarded,myarray)]==1){
  106.      successIfChange++; //success counter
  107.   }
  108. }
  109. //Print results, if the algorithm is right shoud be around 33% and 66%
  110. double total= (successIfNotChange/NUMBER_OF_TRIES) *100;
  111. println "Success rate if user do not change his mind  "+total+" %";
  112.  
  113. double total1= (successIfChange/NUMBER_OF_TRIES) *100;
  114. println "Success rate if user  change his mind "+total1+" %";
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