Monty Hall problem

montyhall.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import random
import multiprocessing


def gen_case():
    return ['goat' if e else 'car' for e in random.sample(range(3), 3)]


def open_goat(case, choice):
    for i, e in enumerate(case):
        if i != choice and e == 'goat':
            return i


def solve(switch):
    """Return True if you win the car."""
    case = gen_case()
    choice = random.randint(0, 2)
    goat = open_goat(case, choice)
    other = (set([choice, goat]) ^ set(range(3))).pop()
    return case[other if switch else choice] == 'car'


def probability(runs, switch):
    wins = 0
    for _ in range(runs):
        wins += solve(switch)
    print('probability={}, switch={}'.format(float(wins) / runs * 100, switch))


def main():
    t = multiprocessing.Process(target=probability, args=[100000, True])
    t.start()
    probability(100000, False)
    t.join()


if __name__ == '__main__':
    main()