1-Hour Pair Programming Interview Problems

What Companies Actually Ask (Not LeetCode)

Based on real 1-hour coding interviews at fintech/payment companies like Ziina, Stripe, Square, etc.

All Problems (Optimized for Interview Success)

🔥 Core Problems (Must Know - 70%+ of interviews)

Problem 1: Payment Rate Limiter - rate_limiter.py

• Prevent payment fraud/abuse - 15-20 minutes

Problem 2: Circuit Breaker - circuit_breaker.py

• Protect against external service failures - 15-20 minutes

Problem 3: Money Handler - money_handler.py

• Precise decimal arithmetic for payments - 15-20 minutes

Problem 4: API Client with Retries - api_client.py

• Reliable external API integration - 20-25 minutes

Problem 5: Event Sourcing - event_sourcing.py

• Transaction audit trail and state reconstruction - 25-30 minutes

Problem 6: Saga Pattern - saga_pattern.py

• Distributed transaction coordination with rollback - 25-30 minutes

⚡ Common Problems (50%+ of interviews)

Problem 7: Transaction Cache - transaction_cache.py

• Cache recent transactions with expiry - 15-20 minutes

Problem 8: Payment Queue - payment_queue.py

• Process payments with priorities - 20-25 minutes

Problem 9: Webhook Delivery System - webhook_delivery.py

• Reliable delivery with retries - 20-25 minutes

🎯 Advanced Problems (30%+ of interviews)

Problem 10: Duplicate Detector - duplicate_detector.py

• Prevent duplicate transactions in real-time - 20-25 minutes

Problem 11: Idempotency Handler - idempotency_handler.py

• Prevent duplicate payment processing - 15-20 minutes

Interview Format (60 minutes)

• 5 min: Problem clarification
• 35 min: Core implementation (pair programming)
• 15 min: Edge cases & optimization
• 5 min: Discussion & questions

What They're Looking For

1. Clean code while thinking out loud
2. Edge case handling (timeouts, failures)
3. Simple solutions that work
4. Good collaboration during pairing
5. Testing mindset (how would you test this?)

Each problem includes:

• ✅ Real-world business context
• ✅ Starter code structure
• ✅ Test cases to guide you
• ✅ Common follow-up questions
• ✅ Expected time to complete