[LeetCode&Python] Problem 860. 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 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(object):
      def lemonadeChange(self, bills):
          """
          :type bills: List[int]
          :rtype: bool
          """
          five=0
          ten=0
          for b in bills:
              if b==10:
                  if five==0:
                      return False
                  five-=1
                  ten+=1
              elif b==20:
                  if five>0 and ten>0:
                      five-=1
                      ten-=1
                  elif ten==0:
                      if five>=3:
                          five-=3
                      else:
                          return False
                  else:
                      return False
              else:
                  five+=1
  
          return True