How to resolve the algorithm Monty Hall problem step by step in the Ruby programming language

Published on 12 May 2024 09:40 PM

How to resolve the algorithm Monty Hall problem step by step in the Ruby programming language

Table of Contents

Problem Statement

Suppose you're on a game show and you're given the choice of three doors. Behind one door is a car; behind the others, goats. The car and the goats were placed randomly behind the doors before the show.

After you have chosen a door, the door remains closed for the time being. The game show host, Monty Hall, who knows what is behind the doors, now has to open one of the two remaining doors, and the door he opens must have a goat behind it. If both remaining doors have goats behind them, he chooses one randomly. After Monty Hall opens a door with a goat, he will ask you to decide whether you want to stay with your first choice or to switch to the last remaining door. Imagine that you chose Door 1 and the host opens Door 3, which has a goat. He then asks you "Do you want to switch to Door Number 2?"

Is it to your advantage to change your choice?

The player may initially choose any of the three doors (not just Door 1), that the host opens a different door revealing a goat (not necessarily Door 3), and that he gives the player a second choice between the two remaining unopened doors.

Run random simulations of the Monty Hall game. Show the effects of a strategy of the contestant always keeping his first guess so it can be contrasted with the strategy of the contestant always switching his guess. Simulate at least a thousand games using three doors for each strategy and show the results in such a way as to make it easy to compare the effects of each strategy.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Monty Hall problem step by step in the Ruby programming language

This Ruby program simulates the classic Monty Hall game show problem thousands of times to determine the probability of winning with each strategy: staying with your original guess or switching to the other unopened door. . Here's a step-by-step breakdown:

Initializer:

n = 10_000: This sets the number of times the game will be played to 10,000. stay = switch = 0: These variables will store the number of wins for each strategy: staying with the original guess and switching to the other door. Game Loop:

The n.times block runs the game n times. For each iteration:

doors = [:goat, :goat, :car].shuffle: Creates an array of three door labels (goat, goat, car) and shuffles them randomly. guess = rand(3): Randomly selects a door (0, 1, or 2) as the initial guess. begin shown = rand(3) end while shown == guess || doors[shown] == :car: Finds a random unopened door (neither the guess nor containing the car) to be shown as a goat. If the guess is the car (doors[guess] == :car), the stay strategy wins, so stay is incremented by 1. Otherwise, the switch strategy wins because the other unopened door must contain the car, so switch is incremented by 1. Output:

Finally, the program prints the winning percentages for both strategies as a percentage of the total games played. Example Output:

Staying wins 33.33% of the time. Switching wins 66.67% of the time. This output demonstrates the well-known result that switching is the better strategy in the Monty Hall problem, winning two-thirds of the time, while staying (not switching) wins only one-third of the time.

Source code in the ruby programming language

n = 10_000                  #number of times to play

stay = switch = 0           #sum of each strategy's wins

n.times do                  #play the game n times
  
  #the doors reveal 2 goats and a car
  doors = [ :goat, :goat, :car ].shuffle
  
  #random guess
  guess = rand(3)
  
  #random door shown, but it is neither the guess nor the car
  begin shown = rand(3) end while shown == guess || doors[shown] == :car
  
  if doors[guess] == :car
    #staying with the initial guess wins if the initial guess is the car
    stay += 1
  else
    #switching guesses wins if the unshown door is the car
    switch += 1
  end
  
end

puts "Staying wins %.2f%% of the time."   % (100.0 * stay   / n)
puts "Switching wins %.2f%% of the time." % (100.0 * switch / n)


  

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