Problem Statement

At a cola stand, each cola 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 cola 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 ith customer pays, return true if you can provide every customer with the correct change, or false otherwise. Input: Example 1: Input: bills = [5,5,5,10,20], ouput = true Example 2: Input: bills = [5,5,10,10,20], ouput = false Output: Example 1: Output: 2 Example 2: Output: 1