LemonadeChange.java

package easy;
/**
 * ClassName: LemonadeChange.java
 * Author: chenyiAlone
 * Create Time: 2019/5/24 13:58
 * Description: No.860
 * 思路:
 *      1. 每个人要花费 5 块钱，能够用于找钱的只有 5, 10 块两种
 *      2. 贪心地使用最大面额的钱进行找零
 *
 *
 * 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.
 *
 */
public class LemonadeChange {
    public boolean lemonadeChange(int[] bills) {
        int fives = 0, tens = 0;
        for (int x : bills) {
            if (x == 5) {
                fives ++;
            } else if (x == 10 && fives > 0) {
                fives --;
                tens ++;
            } else {
                int t = x - 5;
                if (tens > 0) {
                    tens --;
                    t -= 10;
                }
                while (t > 0 && fives > 0) {
                    fives --;
                    t -= 5;
                }
                if (t > 0)
                    return false;
            }
        }
        return true;
    }
}