Payment strategy pattern in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the role of the Payment Strategy interface

In the Payment Strategy pattern, what is the primary role of the Payment Strategy interface?

A Stores user payment details securely in the system database.

B Defines a common method for all payment types to implement, enabling interchangeable payment algorithms.

C Handles the user interface for payment input and confirmation.

D Manages the transaction logs and audit trails for payments.

💡 Hint

Think about how different payment methods can be swapped without changing the client code.

The Payment Strategy interface defines a common method that all payment types implement. This allows the system to use different payment algorithms interchangeably without changing the client code.

❓ Architecture

intermediate

Identifying components in a Payment Strategy pattern design

Which of the following components is NOT typically part of a Payment Strategy pattern design?

A A database schema for storing payment transaction history.

B A context class that uses a payment strategy to process payments.

C Concrete payment classes implementing the payment interface.

D A payment strategy interface defining the payment method.

💡 Hint

Focus on design pattern components, not data storage.

The Payment Strategy pattern focuses on defining payment algorithms and their interchangeable use. Database schema for storing transactions is outside the pattern's scope.

❓ scaling

advanced

Scaling payment processing with the Strategy pattern

When scaling a payment system using the Payment Strategy pattern, which approach best supports adding new payment methods without downtime?

A Deploy new payment strategy implementations as separate microservices and use a service registry for discovery.

B Hardcode all payment methods in a single monolithic application and update it for each new method.

C Store all payment logic in the database and execute it via stored procedures.

D Use a single payment strategy class with conditional statements for all payment types.

💡 Hint

Consider modularity and independent deployment for scaling.

Deploying payment strategies as separate microservices allows independent updates and scaling without downtime, aligning with the Strategy pattern's modularity.

❓ tradeoff

advanced

Tradeoffs of using the Payment Strategy pattern

What is a common tradeoff when using the Payment Strategy pattern in a payment processing system?

A Inability to add new payment methods without changing existing code.

B Reduced flexibility because all payment methods are hardcoded in one place.

C Increased code complexity due to multiple classes versus improved flexibility and maintainability.

D Slower payment processing because strategies must be compiled at runtime.

💡 Hint

Think about the balance between design complexity and benefits.

The Payment Strategy pattern introduces more classes and interfaces, increasing complexity, but it improves flexibility and maintainability by allowing easy addition of new payment methods.

❓ component

expert

Determining the output of a Payment Strategy pattern code snippet

Given the following simplified code snippet, what will be the output when executing the payment process? class PaymentStrategy: def pay(self, amount): pass class CreditCardPayment(PaymentStrategy): def pay(self, amount): return f"Paid {amount} using Credit Card" class PayPalPayment(PaymentStrategy): def pay(self, amount): return f"Paid {amount} using PayPal" class PaymentContext: def __init__(self, strategy): self.strategy = strategy def execute_payment(self, amount): return self.strategy.pay(amount) context = PaymentContext(CreditCardPayment()) result = context.execute_payment(100) print(result)

LLD

class PaymentStrategy:
    def pay(self, amount):
        pass

class CreditCardPayment(PaymentStrategy):
    def pay(self, amount):
        return f"Paid {amount} using Credit Card"

class PayPalPayment(PaymentStrategy):
    def pay(self, amount):
        return f"Paid {amount} using PayPal"

class PaymentContext:
    def __init__(self, strategy):
        self.strategy = strategy
    def execute_payment(self, amount):
        return self.strategy.pay(amount)

context = PaymentContext(CreditCardPayment())
result = context.execute_payment(100)
print(result)

A AttributeError because strategy has no pay method

B Paid 100 using PayPal

C TypeError because pay method is not implemented

D Paid 100 using Credit Card

💡 Hint

Look at which payment strategy instance is passed to the context.

The PaymentContext is initialized with CreditCardPayment, so calling execute_payment(100) returns 'Paid 100 using Credit Card'.