A860-Lemonade-Change

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 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.

我的解法

实现代码

class Solution {
public:
    bool lemonadeChange(vector<int>& bills) {
        int D5 = 0, D10 = 0;
        for (int bill : bills){
            if (bill == 5)
                D5++;
            if (bill == 10){
                if (D5 == 0)
                    return false;
                else{
                    D5--;
                    D10++;
                }
            }
            if (bill == 20){
                if (D5 > 0 && D10 > 0){
                    D5--;D10--;
                }
                else if (D5 >= 3)
                    D5 -= 3;
                else
                    return false;
            }
        }
        return true;
    }
};