Leetcode: Lemonade Change

Lemonade Change



Similar Problems:


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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


  • Solution:
// Blog link: https://code.dennyzhang.com/lemonade-change
// Basic Ideas:
//   For $5, no need for change. 
//   For $20, we can't use it for the following customer
// Complexity: Time O(n), Space O(1)
func lemonadeChange(bills []int) bool {
    count_f, count_t := 0, 0
    for _, bill := range bills {
        if bill == 5 { 
            count_f++
        } else {
            if bill == 10 {
                if count_f == 0 { return false }
                count_f, count_t = count_f-1, count_t+1
            } else {
                // bill == 20
                if count_f == 0 { return false }
                count_f--
                if count_t != 0 {
                    count_t--
                } else {
                    if count_f >= 2 {
                        count_f-=2
                    } else {
                        return false
                    }
                }
            }
        }
    }
    return true
}
linkedin
github
slack

Share It, If You Like It.

Leave a Reply

Your email address will not be published.