890 Lemonade Change

Lemonade Change

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 do not have any change in hand at first.

Given an integer array bills where bills[i] is the bill the ith customer pays, return true if you can provide every customer with the correct change, or false otherwise.

 

Example 1:

**Input:** bills = [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:** bills = [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 not give the change of $15 back because we only have two $10 bills.
Since not every customer received the correct change, the answer is false.

 

Constraints:

1 <= bills.length <= 105
bills[i] is either 5, 10, or 20.

class Solution:
    def lemonadeChange(self, bills: List[int]) -> bool:
        intake = [0,0,0]

        outgoing = 0
        for k in bills:
            #print(intake, outgoing)
            if k == 5:
                intake[0] += 1
            if k == 10:
                intake[1] += 1
            if k == 20:
                intake[2] += 1
            to_return = (k - 5)

            if to_return == 0:
                continue
            if to_return == 5:
                if intake[0] > 0:
                    intake[0] -= 1
                    continue
                else:
                    return False
            
            if to_return == 15:
                if intake[1] >= 1 and intake[0] >= 1:
                    intake[0] -= 1
                    intake[1] -= 1
                    continue
                if intake[0] >= 3:
                    intake[0] -= 3
                    continue
                else:
                    return False
        return True
            
            
        return outgoing < intake