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.
Example 1:
Input: [5,5,5,10,20]
Output: true
Explanation: 
From the first 3 customers, we collect three $5 bills in order.
From the fourth customer, we collect a $10 bill and give back a $5.
From the fifth customer, we give a $10 bill and a $5 bill.
Since all customers got correct change, we output true.
Example 2:
Input: [5,5,10]
Output: true
Example 3:
Input: [10,10]
Output: false
Example 4:
Input: [5,5,10,10,20]
Output: false
Explanation: 
From the first two customers in order, we collect two $5 bills.
For the next two customers in order, we collect a $10 bill and give back a $5 bill.
For the last customer, we can't give change of $15 back because we only have two $10 bills.
Since not every customer received correct change, the answer is false.
Note:
0 <= bills.length <= 10000
bills[i] will be either 5, 10, or 20.
class Solution:
    def lemonadeChange(self, bills: List[int]) -> bool:
        five, ten = 0, 0 
    
        for bill in bills:
            if bill == 5:
                five += 1
            elif bill == 10:
                five -= 1
                ten += 1
            # now last two cases handle if it is a 20
            # if we have a ten give that and one five
            elif ten > 0:
                five -= 1
                ten -= 1
            # last option is to give 3 fives 
            else:       
                five -= 3
            # check if five is under zero then return false
            if five < 0: 
                return False 
        return True

class Solution:
    def lemonadeChange(self, bills: List[int]) -> bool:
        five, ten = 0, 0 
    
        for bill in bills:
            if bill == 5:
                five += 1
            elif bill == 10:
                five -= 1
                ten += 1
            # now last two cases handle if it is a 20
            # if we have a ten give that and one five
            elif ten > 0:
                five -= 1
                ten -= 1
            # last option is to give 3 fives 
            else:       
                five -= 3
            # check if five is under zero then return false
            if five < 0: 
                return False 
        return True
