Range Query Interview Patterns
Range query problems appear frequently in competitive programming and technical interviews. Knowing which data structure to reach for – and […]
Algorithms, Coding Interview Questions, Data Structures
Algorithms, Coding Interview Questions, Monotonic Queue, Queue
Queue and Deque Interview Patterns
Monotonic Deque Pattern – Sliding Window Maximum LeetCode 239. Given an array and window size k, return the maximum in
Design, System Design
Access Control System Low-Level Design
Core Models: ACL, RBAC, ABAC, ReBAC Access control models define how permissions are assigned and evaluated. Each has different tradeoffs
Algorithms, Coding Interview Questions, Math
Probability and Statistics Interview Patterns
Core Probability Concepts Probability questions test your ability to reason about uncertainty and expected behavior. Three concepts appear repeatedly in
System Design
Low-Level Design: Workflow Engine – DAG Execution, Step Retry, and State Persistence (2025)
Low-Level Design: Workflow Engine A workflow engine executes directed acyclic graphs (DAGs) of steps, handling parallelism, retries, and failure propagation.
System Design
System Design: A/B Testing Platform – Experiment Management, Assignment, and Statistical Analysis (2025)
System Design: A/B Testing Platform An A/B testing platform lets product teams run controlled experiments – assigning users to variants,
Algorithms
Advanced Array Interview Patterns: Prefix Sum, Difference Array, and Kadane’s Algorithm (2025)
Advanced Array Interview Patterns Mastering a handful of array techniques unlocks dozens of LeetCode problems. This guide covers the six
System Design
Low-Level Design: Digital Library System – Catalog, Borrowing, Reservations, and DRM (2025)
Core Entities License Management Unlike physical books, digital copies can support multiple simultaneous loans up to a licensed limit. The
System Design
Low-Level Design: Code Review Tool – Diffs, Comments, Approvals, and CI Integration (2025)
Core Entities Diff Computation Server-side diff using the Myers diff algorithm (also used by git). Output stored as unified diff
Algorithms
Advanced Stack Interview Patterns: Monotonic Stack, Calculator, and Expression Parsing (2025)
Monotonic Stack Review A monotonic stack maintains elements in strictly increasing or decreasing order. Increasing monotonic stack: pop when the
Algorithms
Advanced Linked List Interview Patterns: Reversal, Merge, Clone, and LRU Cache (2025)
Reverse Linked List: Iterative, Recursive, and K-Groups Reversing a linked list (LC 206) is the foundational operation. Iterative: maintain prev=None,
System Design
Low-Level Design: Recommendation Engine – Collaborative Filtering, Content-Based, and Hybrid (2025)
Core Entities and Schema The recommendation engine centers on four entities. User: user_id, preferences JSONB, created_at. Item: item_id, category, features
Algorithms
Concurrency and Threading Interview Patterns: Locks, Semaphores, and Deadlock Prevention (2025)
Thread Safety Fundamentals A race condition occurs when two threads read and write shared state concurrently without synchronization, producing non-deterministic
System Design
Low-Level Design: API Rate Limiter – Token Bucket, Sliding Window, and Distributed Throttling
Core Entities Two primary entities drive the design: Token Bucket Algorithm Tokens refill at rate r tokens/second up to capacity
Algorithms
Priority Queue and Monotonic Queue Patterns: Sliding Window Maximum, Top-K, and Scheduling (2025)
Sliding Window Maximum – Monotonic Deque (LC 239) O(n) solution using a monotonic decreasing deque storing indices. Each element is