Dynamic Programming on Grids: Unique Paths, Minimum Path Sum, and Dungeon Game (2025)
5 min read Grid DP Fundamentals Grid DP problems define a 2D state space where dp[i][j] represents some optimum property at cell (i, […] Read article
Algorithms
System Design
System Design: Drone Delivery Platform — Fleet Management, Route Planning, and Airspace Coordination
6 min read Requirements A drone delivery platform dispatches autonomous drones to deliver packages from warehouses or stores to customer addresses. Core challenges: Read article
System Design
Low-Level Design: Parking Lot System — Space Management, Ticketing, and Dynamic Pricing
6 min read Core Entities ParkingLot: lot_id, name, address, total_floors, total_spaces, open_time, close_time, timezone. ParkingFloor: floor_id, lot_id, floor_number, total_spaces, available_spaces. ParkingSpace: space_id, floor_id, Read article
Algorithms
Advanced Tree Interview Patterns: Serialization, LCA, Path Problems, and BST Operations (2025)
6 min read Tree Pattern Overview Tree problems test recursive thinking and the ability to combine top-down and bottom-up information. Most tree problems Read article
System Design
System Design: IoT Data Platform — Device Ingestion, Time-Series Storage, and Real-Time Alerting
6 min read Requirements An IoT data platform ingests telemetry from millions of connected devices — sensors, smart meters, industrial equipment, wearables — Read article
System Design
Low-Level Design: Gym Membership and Access Control System — Plans, Check-In, and Class Booking
4 min read Core Entities Member: member_id, user_id, first_name, last_name, email, phone, photo_url, join_date, status (ACTIVE, SUSPENDED, CANCELLED, FROZEN), emergency_contact. MembershipPlan: plan_id, name Read article
Algorithms
Advanced Binary Search Interview Patterns: Search Space Reduction and Parametric Search (2025)
6 min read Binary Search Beyond Sorted Arrays Binary search is not just for sorted arrays. The generalized binary search applies to any Read article
System Design
System Design: Analytics Dashboard — Real-Time Metrics, Aggregation Pipeline, and Query Engine
5 min read Requirements An analytics dashboard lets users visualize business metrics: revenue over time, active users, conversion rates, funnel analysis, A/B test Read article
System Design
Low-Level Design: Fleet Management System — Vehicle Tracking, Maintenance, and Route Optimization
5 min read Core Entities Vehicle: vehicle_id, vin (unique), make, model, year, type (SEDAN, VAN, TRUCK, ELECTRIC), status (AVAILABLE, ASSIGNED, IN_MAINTENANCE, OUT_OF_SERVICE), current_driver_id, Read article
Algorithms
Advanced Linked List Interview Patterns: Reversal, Cycle Detection, and Merge Operations (2025)
5 min read Why Linked Lists in 2025? Linked list problems test pointer manipulation, in-place operations with O(1) space, and the two-pointer (fast/slow) Read article
System Design
System Design: Content Delivery Network (CDN) — Edge Caching, Routing, and Cache Invalidation
6 min read What is a CDN and Why Does It Matter? A CDN is a geographically distributed network of edge servers that Read article
System Design
Low-Level Design: Online Judge System — Submission Processing, Sandboxed Execution, and Scoring
5 min read Core Entities Problem: problem_id, title, slug, difficulty (EASY, MEDIUM, HARD), statement_markdown, constraints, time_limit_ms, memory_limit_mb, tags (array), is_active. TestCase: tc_id, problem_id, Read article
Algorithms
Sorting Algorithms for Interviews: Merge Sort, Quick Sort, Heap Sort, and Custom Comparators (2025)
5 min read Which Sorting Algorithm for Interviews? You rarely implement a sorting algorithm from scratch in interviews — Python’s sorted() and Java’s Read article
System Design
System Design: Payment Gateway — Authorization, Settlement, Idempotency, and Fraud Prevention
5 min read Requirements A payment gateway processes card transactions between merchants and issuing banks. Core flow: customer enters card details → merchant Read article
System Design
Low-Level Design: Warehouse Management System — Receiving, Put-Away, Picking, and Shipping
5 min read Core Entities Warehouse: warehouse_id, name, address, total_locations, is_active. Location: location_id, warehouse_id, zone (RECEIVING, STORAGE, STAGING, SHIPPING), aisle, bay, level, bin, Read article