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.
Since not every customer received correct change, the answer is false.
Note:
0 <= bills.length <= 10000bills[i]will be either5,10, or20.
// OJ: https://leetcode.com/problems/lemonade-change/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
bool lemonadeChange(vector<int>& bills) {
int five = 0, ten = 0;
for (auto b : bills) {
if (b == 5) {
++five;
} else if (b == 10) {
if (!five) return false;
--five;
++ten;
} else {
if (five && ten) {
--five;
--ten;
} else if (five >= 3) {
five -= 3;
} else {
return false;
}
}
}
return true;
}
};