Procedural illustration of the Monty Hall problem

montyhall.rs

use rand::{thread_rng, Rng};

const DOORS: u32 = 3;
const ROUNDS: u32 = 1000000;
const SWITCH: bool = true;

fn main() {
	if DOORS < 3 {
		panic!("Doesn't work for fewer than 3 doors.");
	}

	println!(
		"{} doors, {} rounds, {} player",
		DOORS,
		ROUNDS,
		if SWITCH { "switching" } else { "non-switching" }
	);

	let mut wins = 0;

	for _ in 0..ROUNDS {
		// host picks the winning door
		let winning = thread_rng().gen_range(0..DOORS);
		// player guesses
		let guess = thread_rng().gen_range(0..DOORS);

		// host opens DOORS-2 non-winning doors;
		// the player's guess and the winning door remain closed
		let mut other_closed = winning;
		// if player happened to guess correctly, a different random door will stay closed
		while other_closed == guess {
			other_closed = thread_rng().gen_range(0..DOORS);
		}
		// 2 doors always stay closed;
		// at this point, `guess` and `other_closed` contain 2 distinct numbers

		// player either switches to the other closed door, or sticks with their guess
		let final_choice = if SWITCH { other_closed } else { guess };
		if final_choice == winning {
			wins += 1;
		}
	}

	println!(
		"{} wins -- {}% win rate",
		wins,
		(100.0 * (wins as f32) / (ROUNDS as f32)).round() as i32
	);
}