860. Lemonade Change

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.

Runtime: 56 ms, faster than 100.00% of JavaScript online submissions for Lemonade Change.

/**
 * @param {number[]} bills
 * @return {boolean}
 */
var lemonadeChange = function(bills) {
    if (bills.length < 1) {
        return false;
    }
    if (bills[0] > 5) {
        return false;
    }
    let sumFive = 1;
    let sumTen = 0;
    let i = 1;
    for (; i < bills.length; i++) {
        if (bills[i] === 5) {
            sumFive++;
        } else if (bills[i] === 10) {
            if (sumFive < 1) {
                return false;
            }
            sumFive--;
            sumTen++;
        } else if (bills[i] === 20) {
            if (sumTen > 0 && sumFive > 0) {
                sumTen--;
                sumFive--;
            } else if (sumFive > 2) {
                sumFive -= 3;   
            } else {
                return false;
            }
        }
    }
    return true;
};