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 510, 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

      

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