Diego's Puzzle

icecream.py

"""
Problem:
An icecream vendor starts her shift with an empty box of change. She sells icecreams for 5€ per unit.
Customers show up one by one and pay with bills of either 5€, 10€, 20€ or 50€.
Depending on the order of customers and the bills they give, she might or might not become unable to process a transaction at some point.
Task: write a function icecream that takes an array of integers representing the suite of bills that each customer gives.
The function must return a boolean that indicates whether the seller can fullfil all customers purchases.
"""

import unittest

ICECREAM_PRICE = 5


def icecream(*bills):
    change = {}
    for cash_in in bills:
        change.update({cash_in: change.get(cash_in, 0) + 1})

        cash_back = cash_in - ICECREAM_PRICE

        for bill in (50, 20, 10, 5):
            nb_bills = min(change.get(bill, 0), cash_back // bill)

            if nb_bills == 0:
                continue

            change.update({bill: change.get(bill) - nb_bills})
            cash_back -= nb_bills * bill

        if cash_back > 0:
            return False

    return True


class TestIcecream(unittest.TestCase):
    def test(self):
        self.assertTrue(icecream(5))
        self.assertTrue(icecream(5, 10))
        self.assertTrue(icecream(5, 5, 5, 10, 10, 20))
        self.assertTrue(icecream(5, 10, 5, 10, 5, 20, 5, 10, 5, 10, 5, 20, 5, 50))

        self.assertFalse(icecream(10))
        self.assertFalse(icecream(5, 20))
        self.assertFalse(icecream(5, 10, 10))


if __name__ == "__main__":
    """ Usage: python3 puzzle.py """
    unittest.main()