860. 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 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 <= 105
• bills[i] is either 5, 10, or 20.

Related Topics

贪心

数组

👍 651

👎 0

解法

# leetcode submit region begin(Prohibit modification and deletion)
from collections import defaultdict


class Solution:
    def lemonadeChange(self, bills: List[int]) -> bool:
        change = defaultdict(int)

        for i, bill in enumerate(bills):
            if bill == 5:
                change[5] += 1
            elif bill == 10:
                if change[5] > 0:
                    change[5] -= 1
                    change[10] += 1
                else:
                    return False
            else:
                if change[10] > 0 and change[5] > 0:
                    change[10] -= 1
                    change[5] -= 1
                elif change[5] > 2:
                    change[5] -= 3
                else:
                    return False

        return True

        
# leetcode submit region end(Prohibit modification and deletion)

复杂度分析

• 时间复杂度 O(N)
• 空间复杂度 O(1)