Playing around with the Prisoner Hat Riddle (http://bit.ly/2hmNSav)

prisoner_hat_riddle.py

"""Playing around with the Prisoner Hat Riddle (http://bit.ly/2hmNSav)

"""
import random


def make_hats(n_people):
    """Return a list of random black or white hats."""
    return [random.randint(0, 1) for _ in range(n_people)]


def count_blacks(hats):
    """Return a list of the number of black hats each person can see."""

    # person at end of line can't see any black hats
    blacks_count = 0
    blacks = []
    for hat in reversed(hats):
        blacks.append(blacks_count)
        blacks_count += hat

    blacks.reverse()
    return blacks


def make_guesses(blacks):
    """Make the aliens happy."""

    guesses = []
    remaining_parity = None
    for index, count in enumerate(blacks):

        parity = count % 2

        # back of line uses parity as guess
        if not index:
            guess = parity
            remaining_parity = parity

        # if previous guess was
        else:
            if remaining_parity == parity:
                guess = 0
            else:
                guess = 1
                remaining_parity = int(not remaining_parity)

        guesses.append(guess)

    return guesses


def circle(value):
    """Format the hat for printing in terminal."""
    if value:
        return u"\u25CF"
    else:
        return u"\u25CB"


def simulate(n_people):
    """Do one run of the "Prisoner Hat Riddle" (http://bit.ly/2hmNSav)"""

    hats = make_hats(n_people)
    blacks = count_blacks(hats)
    guesses = make_guesses(blacks)

    print ''.join(circle(_) for _ in hats)
    print ''.join(circle(_) for _ in guesses)
    print ''


if __name__ == '__main__':

    for i in range(10):
        simulate(79)