7 min read Core Requirements A digital wallet holds a user’s balance and enables peer-to-peer transfers. Key operations: add money (top-up from a […] Read article
7 min read Why Resilience Patterns? In a microservices architecture, service A calls service B which calls service C. If C is slow Read article
6 min read When Math Problems Appear Math interview problems test number theory, combinatorics, and modular arithmetic. Common patterns: prime checking and sieve, Read article
7 min read Core Entities Course: course_id, title, description, instructor_id, category, level (BEGINNER, INTERMEDIATE, ADVANCED), language, price, published_at, status (DRAFT, PUBLISHED, ARCHIVED), total_enrolled. Read article
6 min read Choosing the Right Algorithm Unweighted graph (or all weights equal): BFS gives the shortest path in O(V+E). Weighted graph, non-negative Read article
7 min read Core Entities Restaurant: restaurant_id, name, address, lat, lng, cuisine_type, rating, is_open, prep_time_minutes (average). MenuItem: item_id, restaurant_id, name, description, price, category, Read article
7 min read Overview An ad server matches advertisers’ ads to available ad slots on publisher pages in real time. The two main Read article
6 min read Core Entities Hotel: hotel_id, name, address, city, star_rating, amenities (JSON), check_in_time, check_out_time. RoomType: room_type_id, hotel_id, name (STANDARD, DELUXE, SUITE), max_occupancy, Read article
6 min read What is Event Sourcing? In traditional systems, the database stores the current state: the orders table has one row per Read article
5 min read Core Interval Pattern Interval problems involve ranges [start, end] and typically ask: merge overlapping intervals, find gaps, count the minimum Read article
6 min read What is Multi-Tenancy A multi-tenant SaaS serves multiple customers (tenants) from the same shared infrastructure. Each tenant’s data must be Read article
6 min read Problem and Naive DP LIS: find the length of the longest strictly increasing subsequence of an array. Elements of the Read article
7 min read Core Entities Plan: plan_id, name, billing_cycle (MONTHLY, ANNUAL, WEEKLY), price_cents, currency, trial_days, features (JSON). Subscription: subscription_id, customer_id, plan_id, status (TRIALING, Read article
7 min read Problem Scope Given a prefix typed by the user, return the top-K (typically 5-10) suggestions ranked by relevance. Used in Read article
6 min read Tree DP Pattern Many tree problems require computing an answer that depends on both subtrees. The key pattern: define a Read article
