Problem

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.

Pre analysis

Will simulate each case, cannot sort it since order would change and result in wrong answer, additionally if 20 is case it could be either 5+10 or 5+5+5;