QUESTION:

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.
``````

Note:

• `0 <= bills.length <= 10000`
• `bills[i]` will be either `5`, `10`, or `20`.

EXPLANATION:

1.收到5元，那么就直接收下。

2.收到19元，找回5元

3.收到20，找零10+5 或者是5+5+5

SOLUTION:

``````class Solution {
int[] cash = new int[3];
for(int i=0;i<bills.length;i++){
switch (bills[i]){
case 5:
cash[0]++;
break;
case 10:
cash[0]--;
cash[1]++;
break;
case 20:
if(cash[1]>0&&cash[0]>0){
cash[1]--;
cash[0]--;
}else {
cash[0]-=3;
}
cash[2]++;
break;
}