The Cruscible Journal

Deep dives, design notes, and explanations from the engineers behind the problems.

• Cruscible vs LeetCode: Why Real Infrastructure Beats Mock Environments

  LeetCode taught you algorithms. Cruscible teaches you engineering. Here is why the switch matters for your career.

  2026-05-27

• How to Practice System Design: A Developer's Roadmap from Easy to Expert

  A structured path through 12 system design problems — from retry engines to deployment pipelines. Build real systems, not draw diagrams.

  2026-05-27

• Cruscible: The Platform Where System Design Meets Real Code

  85+ engineering challenges with real Redis, PostgreSQL, and Kafka. Not a browser sandbox — your code runs in actual containers.

  2026-05-27

• Why LLD Practice Matters More Than LeetCode for Real Engineering Jobs

  LeetCode tests pattern recall. LLD tests whether you can actually build production systems. Here's why the industry is shifting.

  2026-05-27

• Url Shortner

  URL shortening sits behind every bit.ly, t.co, youtu.be, and goo.gl link you have ever clicked. The contract is deceptively small:

  2026-05-27 · Try the problem

• Building a Deployment Pipeline Engine with Rollback Support

  Sequential stage advancement, rollback, cancellation, and deployment history — backed by PostgreSQL and Redis

  2026-05-27 · Try the problem

• Building an Indian Railway Reservation System

  Confirmed berths, RAC, Waiting List — with FIFO promotion chains and berth preferences, all in-memory

  2026-05-27 · Try the problem

• Building a Cab Booking System with Ride State Machine

  GPS-based nearby search, Haversine distance, fare calculation, and race-safe ride acceptance — all backed by PostgreSQL

  2026-05-27 · Try the problem

• Building a Load Balancer with Four Routing Algorithms

  Round-robin, weighted, least-connections, and random — all backed by Redis with health-aware routing

  2026-05-27 · Try the problem

• Building a Multi-Floor Parking Lot System

  Manage vehicle parking, ticket issuance, fee calculation, and occupancy tracking with PostgreSQL

  2026-05-27 · Try the problem

• Building a Sliding Window Rate Limiter with Redis

  Protect your APIs from abuse using sorted sets, Lua scripts, and the sliding window algorithm

  2026-05-27 · Try the problem

• Building a Priority Task Queue with Dead-Letter Support

  Redis sorted sets, atomic dequeue with Lua, and a dead-letter queue that catches tasks that can't be saved

  2026-05-27 · Try the problem

• Building an LRU Cache with O(1) Operations

  Implement the classic eviction cache using a doubly-linked list encoded in a key-value store

  2026-05-27 · Try the problem

• Building an Employee Management System in Pure Java

  Master in-memory data structures, multi-dimension indexing, and thread-safe CRUD — no database required

  2026-05-27 · Try the problem

• Building a Circuit Breaker from Scratch

  Stop cascading failures before they take down your entire system — with Redis-backed state and atomic transitions

  2026-05-27 · Try the problem

• Building a Retry Engine with Exponential Backoff

  Handle transient failures gracefully with configurable retries, jitter, and per-operation state tracking

  2026-05-27 · Try the problem