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LeetCode860.Lemonade Change
题目
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 <= 10000
bills[i] will be either 5, 10, or 20.
思路
分类讨论。
代码
class Solution {
public:
bool lemonadeChange(vector<int>& bills) {
int i, j, k, ans = 0;
int a[25];
a[5] = 0;
a[10] = 0;
a[20] = 0;
for(i=0; i<bills.size(); i++) {
j = bills[i] - 5;
if(j > ans) {
return false;
}
if(j == 0) {
ans = ans + 5;
a[5]++;
continue;
}
if(j == 5) {
if(a[5] == 0) {
return false;
}
else {
a[5]--;
a[10]++;
ans+=5;
continue;
}
}
if(a[10]) {
if(a[5]==0) {
return false;
}
a[10]--;
a[5]--;
a[20]++;
ans = ans+=5;
}
else {
if(a[5] <= 2) {
return false;
}
a[5] = a[5] - 3;
ans = ans+=5;
}
}
return true;
}
};