Moody's Software Engineer Interview Experience — Onsite System Design for a Product Inventory Service

System Design

Design a Product Inventory & Pricing Service for an e-commerce platform

1. Functional requirements: get product details, update product price, update inventory when a user places an order.
2. System requirements: this is a read-heavy system, so we needed to discuss the Consistency vs Availability tradeoff, plus authorization for inventory updates.
3. Technical approach discussion: SQL vs NoSQL choice (considering ACID), when to use REST API vs gRPC, a Redis caching layer, using a Bloom Filter to cut down invalid DB queries, and a Master-Replica database architecture.

Follow-up Questions

1. What happens if the entire Redis Cluster goes down? (Testing whether I'd fall back to an application-layer L1 in-memory cache.)
2. How would you optimize when hundreds or thousands of users request the same product at once? (Discussed request batching, merging duplicate requests.)
3. Multiple users order the same item at the same time — how do you handle concurrent inventory decrements? (Discussed write locking and Redis atomic decrement operations.)

Print BST nodes in ascending order

1. Given a BST, print all nodes in ascending order (standard inorder traversal).
2. Follow-up: if the tree has a huge number of nodes, or is an extremely unbalanced skewed tree, what's the problem with a recursive solution? (Testing awareness of stack overflow risk.)
3. Follow-up: what are the alternatives in that case? (Discussed the limits of just increasing stack size, an iterative traversal using an explicit stack, and Morris traversal for O(1) space.)

Longest Subarray with At Most 2 Distinct Elements

1. Given an array, find the length of the longest subarray containing at most two distinct elements.
2. Discussed and implemented a sliding window solution.