lemonadeChange.py

"""
At a lemonade stand, each lemonade costs $5.

Customers are standing in a queue to buy from you, and order one at a time (in the order specified by bills).

Each customer will only buy one lemonade and pay with either a $5, $10, or $20 bill.
You must provide the correct change to each customer, so that the net transaction is that the customer pays $5.

Note that you don't have any change in hand at first.
Return true if and only if you can provide every customer with correct change.

"""


class Solution:
    def lemonadeChange(self, bills: list[int]) -> bool:
        fives = 0
        tens = 0
        for i in bills:
            if i == 5:
                fives += 1
            if i == 10:
                if fives < 1:
                    return False
                else:
                    fives -= 1
                    tens += 1
            if i == 20:
                if tens >= 1 and fives >= 1:
                    tens -= 1
                    fives -= 1
                elif fives >= 3:
                    fives -= 3
                else:
                    return False

        return True