890. Lemonade Change

难度: Easy

题目描述

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.

 

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.

解题思路

代码实现

解决方案

java

class Solution {
    public boolean lemonadeChange(int[] bills) {

        int[] count = new int[3];
        int n = bills.length;
        for (int i = 0; i < n; i++) {
            if (bills[0] != 5) {
                return false;
            } else if (bills[i] == 5) {
                count[0]++;
            } else if (bills[i] == 10) {
                if (count[0] < 1) {
                    return false;
                }
                count[1]++;
                count[0]--;
            } else if (bills[i] == 20) {
                if ((count[0] < 3 && count[0] > 0 && count[1] < 1) || count[0] < 1 || (count[0] == 1 && count[1] < 1)) {
                    return false;
                }
                if (count[1] > 0 && count[0] > 0) {
                    count[1]--;
                    count[0]--;
                    continue;
                }
                count[0]--;
                count[0]--;
                count[0]--;

            }

        }
        return true;

    }
}