860 - Lemonade Change.

Easy

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 <code>i^th</code> 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 $

From the fifth customer, we give a

$10 bill and a $

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 $

For the last customer, we can not give the change of

$15 back because we only have two $

Since not every customer received the correct change, the answer is false.

Constraints:

• <code>1 <= bills.length <= 10⁵</code>

• bills[i] is either 5, 10, or 20.