•SYSTEM DESIGN
Visa System Design Questions
5 distinct system design problems asked at Visa from September 2025 to September 2026, merged from 5 candidate reports. Each one links to a full solution.
Sources: PracHub, LeetCode discussions. Sorted by how often the problem was reported at Visa.
Design E-Commerce Tables and Indexes for Recent-Spend Queries
Design normalized relational tables for an e-commerce system (users, products, orders, order line items) that preserve the price actually charged at purchase time even when product prices change later, and enforce integrity…
Payment system: states, payment methods, durable execution, retries
Design a payment processing system (like Stripe's core) that handles about 10,000 transactions per second between merchants and external payment providers. Support the full lifecycle: authorization (place a hold on funds with low…
Design a notification system
Design a multi-channel notification service (push, email, SMS, in-app) that other services call to notify users. It must accept sudden bursts of millions of notifications with low acknowledgement latency, persist them durably,…
Re-architect your current project for planet scale
Walk through the architecture of a real project you built, end to end: the trigger, components and interfaces, data ownership and storage, deployment, failure handling and your personal contributions. Then redesign it to work at…
Memory allocator (LeetCode 2502 variant)
Design a memory allocator over a fixed array of n units: allocate(size, id) finds the leftmost block of size consecutive free units and assigns it to the id, and free(id) releases all units belonging to that id. Discuss data…
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