leetcode-860-Lemonade-Change

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:

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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:

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Input: [5,5,10]
Output: true

Example 3:

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Input: [10,10]
Output: false

Example 4:

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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.

分析


一杯柠檬水售价5刀,顾客可能会给5刀,10刀,20刀的钞票,刚开始柜台没有零钱,每个顾客只买一杯柠檬水,问整个过程柜台会不会出现找不出零钱的情况。

一次遍历即可,如果是5刀,不需要找钱,如果是10刀,查看5刀的钞票的数量,如果是20刀,先找10刀的钞票,再找5刀的钞票。

解决方案1(Java)


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class Solution {
public boolean lemonadeChange(int[] bills) {
int fiveCount = 0, tenCount = 0;
for (int i = 0; i < bills.length; i++) {
if (bills[i] == 5) {
fiveCount++;
} else if (bills[i] == 10) {
if (fiveCount > 0) {
tenCount++;
fiveCount--;
} else {
return false;
}
} else {
if (tenCount > 0 && fiveCount > 0) {
tenCount--;
fiveCount--;
} else if(fiveCount >= 3) {
fiveCount = fiveCount - 3;
} else {
return false;
}
}
}
return true;
}
}

题目来源