[LeetCode] Problem 860 - Lemonade Change

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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

No.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.

No.2

Input: [5,5,10]

Output: true

No.3

Input: [10,10]

Output: false

No.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.

Code

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public boolean lemonadeChange(int[] bills) {
    int five = 0;
    int ten = 0;

    for (int bill : bills) {
        if (bill == 5)
            five++;
        else if (bill == 10) {
            ten++;
            five--;
        }
        else if (ten > 0) {
            ten--;
            five--;
        }
        else 
            five -= 3;

        if (five < 0)
            return false;
    }

    return true;
}