9 tracks · one way of explaining
Engineering skills, compounded.
Visual, step-by-step explanations of DSA, system design, AI and ML systems, DevOps and career roadmaps — built so hard ideas stick before your next interview.
Free lessons in every track. No card required.
Welcome back. Pick a track and keep going.
Trapping Rain Water
Step 5 / 14Design a URL Shortener
ArchitectureParking Lot
Class diagramHow RAG answers a question
Scene 3 / 7Canary deployments
Rolling outlmax = 2rmax = 3water = 4
1def trap(h):
2 l, r, lmax, rmax, water = 0, len(h) - 1, 0, 0, 0
3 while l < r:
4 if h[l] < h[r]:
5 lmax = max(lmax, h[l])
6 water += lmax - h[l]; l += 1
7 else:
8 rmax = max(rmax, h[r]); r -= 1
Clientbrowser
API gatewayauth · limits
URL servicestateless × N
Cachechecked first
Databaseshort → long
Click eventsqueue → analytics
ID generatorbase62 · no collisions
Read path. A redirect checks the cache first; only a miss falls through to the database, then the cache is filled for next time.
ServiceData storeQueueIn focus
ParkingLot
- levels: List<Level>
+ park(v): Ticket+ unpark(t): Fee
1..*
Level
- spots: List<Spot>
+ findSpot(v): Spot
1..*
«abstract»Spot
- occupied: bool
+ fits(v): bool
CompactSpot
LargeSpot
EVSpot
Why abstract? Each spot type decides what fits. Adding EV charging is a new subclass — ParkingLot never changes. That’s open–closed in practice.
Question
Embed
Vector search
Prompt + LLM
Answer
Vector DB
top-k = 3 nearest chunks
Scene 3The question is now a vector. It’s compared with every chunk in the store, and only the three closest come back to ground the answer.
Story
Commitmain · a3f9c1e
Buildcontainer image
Unit + integration testsall green
Deploy to stagingsmoke tests passed
Canary — 10% of trafficwatching metrics
Production — 100%waiting on gates
Traffic split
canary v2 · 10%stable v1 · 90%
Promotion gatesError rate within thresholdp99 latency unchangedSoak time remaining
If either gate fails, traffic shifts back to v1 automatically — no one gets paged at 3 a.m.
Tracks
Everything you’ll be asked, explained the same way.
01
DSA
Patterns and hard LeetCode problems as step-through visuals.
Step-through players02
Code System Design
Building blocks — caches, rate limiters, queues — implemented in code.
Diagrams + multi-language code03
HLD
Architecture diagrams and case studies for system design rounds.
Architecture + sequence diagrams04
LLD
Class diagrams, design patterns and object-oriented case studies.
Class diagrams + code05
DevOps
Pipelines, containers and clusters, drawn step by step.
Flowcharts + infra diagrams06
AI Engineering
RAG, agents and evaluation — how LLM apps really work.
Animated stories07
ML System Design
Animated stories from raw data to models in production.
Animated stories08
Roadmaps
What to learn, in what order, for the role you want.
Guided paths09
AI System Design
Designing LLM-powered systems: serving, retrieval, guardrails and cost.
Architecture + animated storiesGo further with Aayush
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Mock interview
A realistic DSA or system design round with Aayush — then written feedback on exactly what to fix.
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Career moves, a resume review, a learning plan, or a system you’re designing.
Book a call →How a lesson works
Picture first. Then the steps. Then the code.
01
See the shape
Every lesson opens with a picture — a diagram, a flowchart or an animation — before a single line of code.
02
Step through it
Play, pause and scrub. Each step highlights what changed and why, so you follow the reasoning, not just the answer.
03
Write it yourself
Finish with clean, interview-ready code in several languages, plus the complexity and the follow-ups interviewers ask.
Around 30% of the library is free forever, including starter lessons in every track. Pro unlocks every lesson, animation, step-through player and code walkthrough — plus everything new as it ships.
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Small lessons. Compounding returns.
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