At a lemonade stand(柠檬汁小摊), 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[按规定的顺序]).
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.[所以净交易是顾客支付5美元。]
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 static boolean lemonadeChange(int[] bills) { int fives=0; int tens=0; for (Integer bill:bills){ if (bill==5){//顾客给5块钱时，不用找钱，5块钱个数+1 fives++; }else if(bill==10){//顾客给10块钱的时候，只能找一个5块钱，5块钱数-1,10块钱数+1 tens++; fives--; }else if(tens>0){ //顾客给20块钱的时候，如果手头的零钱有10块钱，给10块和一个5毛钱=15块 tens--; fives--; }else{//顾客给20块钱的时候，如果手头的零钱没有10块钱，给3个5块钱=15块[因为20块钱找钱我们手里只有5,10,20所以只能10+5或者5+5+5] fives-=3; } if (fives<0)return false; } return true; }