LeetCode/LemonadeChange.java at main · saidodil/LeetCode · GitHub

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/**
 * 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 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.
 */

class LemonadeChange {
    public boolean lemonadeChange(int[] theBills) {
        int count5 = 0;  // count of $5 bills in hand
        int count10 = 0; // count of $10 bills in hand

        for (int bill : theBills) {
            if (bill == 5)
                count5++;
            else if (bill == 10) {
                if (count5 > 0) {
                    count5--;
                    count10++;
                } else
                    return false;
            // bill == 20
            } else {
                if (count10 > 0 && count5 > 0) {
                    count10--;
                    count5--;
                } else if (count5 >= 3)
                    count5 -= 3;
                else
                    return false;
            }
        }
        return true;
    }
}