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This is a medium difficulty Software Engineering Fundamentals question, commonly asked during Technical Screen rounds at ZipHQ.

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This question is commonly asked for Software Engineer candidates at ZipHQ during technical interviews.

Implement a Vending Machine | ZipHQ Interview Question

Q: Implement a Vending Machine

This question evaluates object-oriented design, stateful transaction management, inventory control, and algorithmic change-making under resource constraints.

Design and implement the core logic for a vending machine using object-oriented principles.

The machine stores products, accepts bills, tracks the current customer's balance, dispenses an item after selection, and returns change.

Requirements:

Each product has an id, a price in cents, and a remaining quantity.
The machine accepts a fixed set of bill denominations, for example 1, 5, 10, and 20 dollar bills.
insertBill(amount) adds money to the current transaction.
selectProduct(productId) should:
1. verify the product exists and is in stock,
2. verify the customer has inserted enough money,
3. deduct one unit of inventory,
4. compute and dispense change using bills available in the machine,
5. fail gracefully if exact change cannot be made.
cancel() should return the customer's inserted money and reset the transaction.
The implementation should be testable, and you should write tests for key cases such as insufficient funds, exact payment, overpayment, out-of-stock items, and inability to make exact change.

Assume starter code is provided for the main classes, and implement the missing behavior and tests.

Design and implement the core logic for a vending machine using object-oriented principles.

The machine stores products, accepts bills, tracks the current customer's balance, dispenses an item after selection, and returns change.

Requirements:

Each product has an id, a price in cents, and a remaining quantity.
The machine accepts a fixed set of bill denominations, for example 1, 5, 10, and 20 dollar bills.
insertBill(amount) adds money to the current transaction.
selectProduct(productId) should:
1. verify the product exists and is in stock,
2. verify the customer has inserted enough money,
3. deduct one unit of inventory,
4. compute and dispense change using bills available in the machine,
5. fail gracefully if exact change cannot be made.
cancel() should return the customer's inserted money and reset the transaction.
The implementation should be testable, and you should write tests for key cases such as insufficient funds, exact payment, overpayment, out-of-stock items, and inability to make exact change.

Assume starter code is provided for the main classes, and implement the missing behavior and tests.

Implement a Vending Machine

Quick Overview

Solution

Submit Your Answer to Earn 20XP

Implement a Vending Machine

Quick Overview

Solution

Submit Your Answer to Earn 20XP