MontyHall.php

<?php
/**
 * MontyHall.php
 *
 * Example Monty Hall problem simulation.
 * usage: php MontyHall.php
 *
 * @author Maxamilian Demian
 * @link https://www.maxodev.org
 * @link https://github.com/Maxoplata/MontyHall
 */

// The number of times to run for each choice (keep and change will run numberOfRuns times EACH)
$numberOfRuns = 1000000;

$keepWins = 0;
$keepLosses = 0;
$changeWins = 0;
$changeLosses = 0;

// loop numberOfRuns without changing our initial door selection
for ($i = 0; $i < $numberOfRuns; $i++) {
	// pick a winning door between 1 and 3
	$winningDoor = rand(1, 3);

	// player selects a random door between 1 and 3
	$playerDoor = rand(1, 3);

	if ($playerDoor === $winningDoor) {
		// player chose the winning door
		$keepWins++;
	} else {
		// player chose a losing door
		$keepLosses++;
	}
}

// loop numberOfRuns while changing our initial door selection
for ($i = 0; $i < $numberOfRuns; $i++) {
	// pick a winning door between 1 and 3
	$winningDoor = rand(1, 3);

	// player selects a random door between 1 and 3
	$playerDoor = rand(1, 3);

	if ($playerDoor === $winningDoor) {
		// player chose the winning door already, count it as a loss as the player will be changing
		$changeLosses++;
	} else {
		/* if the player HAS NOT chosen the winning door already and they change, they will win
		 * example:
		 * - player chooses door 1
		 * - winning door is door 3
		 * - host opens door 2 showing a goat
		 * - player switches to door 3 and wins
		 *
		 * every variation of this will win since we have already eliminated the aspect of the player
		 * having already picked the winning door
		 */
		$changeWins++;
	}
}

print "Keep Wins/Losses: {$keepWins}/{$keepLosses} (" . (($keepWins / $numberOfRuns) * 100) . "% wins)" . PHP_EOL;
print "Change Wins/Losses: {$changeWins}/{$changeLosses} (" . (($changeWins / $numberOfRuns) * 100) . "% wins)" . PHP_EOL;