Go Simulation of the Monty Hall Problem for N-Doors

montyhall.go

// Monty Hall Problem Simulation

package main

import (
	"fmt"
	"math/rand"
	"time"
)

func play_round(doors int, trade bool) bool {
	var car int
	var initial_choice int
	var monty_leaves int
	var final_choice int
	var victory bool

	// Choose the location of the car
	car = rand.Intn(doors)

	// Contestant chooses a door
	initial_choice = rand.Intn(doors)

	// Monty opens ALL the other doors except one
	if initial_choice != car {
		monty_leaves = car // If the car wasn't chosen, Monty is forced to reveal its location
	} else {
		for {
			monty_leaves = rand.Intn(doors)
			if monty_leaves != initial_choice {
				break
			}
		}
	}

	// monty_leaves is now the door that Monty DIDN'T open
	if trade {
		final_choice = monty_leaves
	} else {
		final_choice = initial_choice
	}
	victory = (final_choice == car)
	return victory
}

func simulation(iterations int, doors int) {
	var games_won_trade, games_won_notrade int
	var victory bool
	var i int = 1

	for i <= iterations {
		victory = play_round(doors, false)
		if victory {
			games_won_notrade += 1
			i += 1
		}
		victory = play_round(doors, true)
		if victory {
			games_won_trade += 1
			i += 1
		}
	}

	fmt.Println("")
	fmt.Println("                  Monty Hall Simulation")
	fmt.Println("---------------------------------------------------------")
	fmt.Println("                  Iterations: ", iterations)
	fmt.Printf("\n     Games won when switching doors: %d (%f%%)", (games_won_trade), (100 * float32(games_won_trade) / float32(iterations)))
	fmt.Printf("\n Games won when NOT switching doors: %d (%f%%)", (games_won_notrade), (100 * float32(games_won_notrade) / float32(iterations)))
}

func main() {
	var iterations int = 1000000
	var doors int = 3
	rand.Seed(time.Now().UnixNano())
	simulation(iterations, doors)
}