Lemonade Change

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- Tag: #array

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 }

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