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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0801_0900.s0860_lemonade_change;

// #Easy #Array #Greedy #Programming_Skills_II_Day_17
// #2022_03_27_Time_2_ms_(90.84%)_Space_75.8_MB_(55.09%)

/**
 * 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 i^th 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 $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:** 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 $5 bill.
 *
 * For the last customer, we can not give the change of $15 back because we only have two $10 bills.
 *
 * Since not every customer received the correct change, the answer is false.
 *
 * **Constraints:**
 *
 * *   1 <= bills.length <= 10⁵
 * *   `bills[i]` is either `5`, `10`, or `20`.
**/
public class Solution {
    public boolean lemonadeChange(int[] bills) {
        int countFive = 0;
        int countTen = 0;
        for (int bill : bills) {
            if (bill == 5) {
                countFive++;
            } else if (bill == 10) {
                if (countFive == 0) {
                    return false;
                }
                countFive--;
                countTen++;
            } else if (bill == 20) {
                if (countFive > 0 && countTen > 0) {
                    countFive--;
                    countTen--;
                } else if (countFive >= 3) {
                    countFive -= 3;
                } else {
                    return false;
                }
            }
        }
        return true;
    }
}