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.
思路：贪心，优先使用10元的去找零钱。
class Solution {
public:
bool lemonadeChange(vector<int>& bills) {
queue<int> q;
int num5 = 0;
int num10 = 0;
for (int i = 0; i < bills.size(); ++i) {
if (bills[i] == 5) {
num5++;
}
else {
int x = bills[i];
if (bills[i] == 20) {
while (bills[i] > 10 && num10 > 0) {
bills[i] -= 10;
num10--;
}
while (bills[i] > 5 && num5 > 0) {
bills[i] -= 5;
num5--;
}
if (bills[i] > 5) {
return false;
}
}
else {
while (bills[i] > 5 && num5 > 0) {
bills[i] -= 5;
num5--;
}
if (bills[i] > 5) {
return false;
}
num10++;
}
}
}
return true;
}
};