Leetcode之Lemonade Change

題目：

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 $20bill.  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.

代碼：

class Solution {
public:
    bool lemonadeChange(vector<int>& bills) {
        int len = bills.size();
    int money[3] = { 0 };
    for (int i = 0; i < len; i++) {
        if (bills[i] == 5) {
            money[0]++;
        }
        else if (bills[i] == 10) {
            if (money[0] == 0)return false;
            else {
                money[0]--;
                money[1]++;
            }
        }
        else {
            if ((money[0] < 3&&money[1] == 0)||(money[1]>=1&&money[0]==0))return false;
            else {
                if(money[1]==0){
                    money[0]-=3;
                }else{
                    money[0]--;
                    money[1]--;}
                
                money[2]++;
            }
        }
    }
    return true;
    }
};

思路：貪心算法分類討論