Problem
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 do not have any change in hand at first.
Given an integer array bills where bills[i] is the bill the ith customer pays, return true if you can provide every customer with the correct change, or false otherwise.
Example 1:
Input: bills = [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: bills = [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 not give the change of $15 back because we only have two $10 bills.
Since not every customer received the correct change, the answer is false.
Constraints:
1 <= bills.length <= 10^5bills[i]is either5,10, or20.
Solution (Java)
class Solution {
public boolean lemonadeChange(int[] bills) {
int countFive = 0;
int countTen = 0;
for (int bill : bills) {
if (bill == 5) {
countFive++;
} else if (bill == 10) {
if (countFive == 0) {
return false;
}
countFive--;
countTen++;
} else if (bill == 20) {
if (countFive > 0 && countTen > 0) {
countFive--;
countTen--;
} else if (countFive >= 3) {
countFive -= 3;
} else {
return false;
}
}
}
return true;
}
}
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).