Lemonade Change (LEETCODE 860)

LeetCode Leetcode Challenge

Handling Change at the Lemonade Stand: A Step-by-Step Guide in Java and Python

Step-by-Step Solution Approach

Managing a lemonade stand might sound simple, but what if you had to ensure you always had the correct change? This problem is an excellent exercise in implementing logic to simulate a real-world scenario using programming. Below is the approach to solve the problem where customers pay with $5, $10, or $20 bills, and you need to ensure you can provide the correct change every time.

Problem Restatement

You are given an array 'bills' where each element represents the bill paid by a customer in a queue. The bills can be $5, $10, or $20, and each lemonade costs $5. You need to determine if you can provide the correct change to every customer.

Step 1: Understand the Constraints

1. You start with no change.
2. Each customer will pay exactly one bill.
3. You need to provide change using the bills you have already collected.

Step 2: Plan the Solution

To solve this, we'll:

• Track the number of $5 and $10 bills we have.
• Iterate through each bill in the array.
• Provide change if needed, using the highest denomination available first (to conserve smaller bills).

Step 3: Implement the Solution in Java & PYTHON

class Solution:
    def lemonadeChange(self, bills):
        five, ten = 0, 0
        
        for bill in bills:
            if bill == 5:
                five += 1
            elif bill == 10:
                if five == 0:
                    return False
                five -= 1
                ten += 1
            else:
                if ten > 0 and five > 0:
                    ten -= 1
                    five -= 1
                elif five >= 3:
                    five -= 3
                else:
                    return False
        return True        

Step 5: Test the Solution

Example 1:

• Input: [5,5,5,10,20]
• Output: true

Example 2:

• Input: [5,5,10,10,20]
• Output: false

Explanation:

• In the first example, you can provide the correct change for all customers.
• In the second example, you cannot give correct change to the last customer.

Conclusion

This problem illustrates the importance of considering different cases and efficiently managing resources (in this case, money). By tracking the count of each bill denomination, we ensure that each transaction is handled correctly.

GITHUB: (FULL CODE)

GITHUB.SMILE_KHAN-JAVA + PYTHON

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