A fun interviewing problem!

coined.py

#!/usr/bin/python
# assumes python 2.7
# Script by JesseBot@linux.com
# 3/2/16
import random
"""
Assume there is a room full of coins and a robot that can interact with them.
The robot picks up each coin and if the coin was heads face up, it flips it to
 tails. If the coin is tails up, the robot tosses the coin into the air. We
 assume the robot is picking up coins at random. Wite a program to give the
 percentage of heads and tails coins when the robot is done. Allow number of
 coins to be given, and also allow iterations to be set, (some tests should
 include what would happen if the interactions were an order of magnitude or
 two larger than amount of coins). Print percentages before and after.
"""


def calculate_start(coins, interactions, num_of_heads_start):
    """Just make sure typing is correct for all these integers and if not,
        just make up a coin number for them. Let's do this."""
    # verify we got integers and if not, just keep on truckin'
    try:
        int(coins)
    except ValueError:
        # this is just for the proof of concept, I could handle this gracefully
        coins = 500
    finally:
        if not interactions:
            interactions = coins * (10**2)
    # more verification
    try:
        int(num_of_heads_start)
    except ValueError:
        # the show must go on...
        num_of_heads_start = coins / 2
    # get starting tails
    num_of_tails_start = coins - num_of_heads_start
    # give starting percentages
    tails_percent = 100 * float(num_of_tails_start)/float(coins)
    heads_percent = 100 * float(num_of_heads_start)/float(coins)
    # let user know what's up
    print "Starting Tails: {0} which is {1} percent".format(num_of_tails_start,
                                                            tails_percent)
    print "Starting Heads: {0} which is {1} percent".format(num_of_heads_start,
                                                            heads_percent)
    return coins, num_of_tails_start, num_of_heads_start, interactions


def calculate_coin_faces(coins=500, interactions=50000,
                         num_of_heads_start=250):
    """Takes three integers: coins, interactions, num_of_heads_start
        and will calculate the resulting percentage of heads and tails facing
        coins. Assume we always flip heads to tails and tails into the air.
        Prints percentage before and after. If nothing given, uses 500 coins,
        50000 interactions, and 250 number of heads to start values."""
    start = calculate_start(coins, interactions, num_of_heads_start)
    coins = start[0]
    tails = start[1]
    heads = start[2]
    interactions = start[3]
    # assume beginning tails
    final_numbers = {'final_heads': heads, 'final_tails': tails}
    # start range calc for interactions and coins (python range is silly)
    total_interactions = interactions + 1
    coins_range = coins + 1
    # begin looping to play with your coins
    for interaction in range(1, total_interactions):
        # grab a random coin off the floor
        rando_coin = random.randint(1, coins_range)
        # if heads
        if rando_coin in range(1, final_numbers['final_heads']):
            final_numbers['final_heads'] -= 1
            final_numbers['final_tails'] += 1
        # if tails
        else:
            flip = random.randint(0, 1)
            if flip == 0:
                final_numbers['final_heads'] += 1
                final_numbers['final_tails'] -= 1
    # calculate percentages
    heads = final_numbers['final_heads']
    tails = final_numbers['final_tails']
    tails_percent = 100 * float(tails)/float(coins)
    heads_percent = 100 * float(heads)/float(coins)
    # tell the user what's up
    print "Ending Tails: {0} which is {1} percent".format(tails,
                                                          tails_percent)
    print "Ending Heads: {0} which is {1} percent".format(heads,
                                                          heads_percent)
    return heads_percent, tails_percent


if __name__ == '__main__':
    while True:
        interactive = raw_input("Would you like an interactive demonstration?" +
                                " (y/n) ")
        if interactive == 'n':
            print "Okie dokie, on with the show, we'll assume 500 coins," + \
                  " 50000 interactions, and 250 heads to start."
            calculate_coin_faces()
            break
        elif interactive == 'y':
            coins = int(raw_input("How many coins? "))
            interactions = int(raw_input("How many interactions should we do? "))
            num_of_heads_start = int(raw_input("How many coins should be heads " +
                                               "to start? "))
            calculate_coin_faces(coins, interactions, num_of_heads_start)
            break
        else:
            print "Please give y or n as an answer."

print "Thanks for playing!"