- Lemonade Change Easy
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Share 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.
思路：字典用来存储各个面值的纸币数量dic[5]dic[10] 遍历bills，5的面值直接dic[5]++,10的面值得看dic[5]是否为0，为0返回False，否则dic[5]--dic[10]++,20面值的分情况讨论
代码：python3
class Solution:
def lemonadeChange(self, bills: List[int]) -> bool:
dic={}
dic[5]=0
dic[10]=0
for index,value in enumerate(bills):
if value==5:
dic[5]+=1
elif value==10:
if dic[5]==0:
return False
else:
dic[10]+=1
dic[5]-=1
elif value==20:
if dic[5]==0:
return False
elif dic[10]==0:
if dic[5]>=3:
dic[5]=dic[5]-3
else:
return False
else:
dic[10]-=1
dic[5]-=1
return True
