Day49
60-day SSE plan
ATM System • Video Streaming • Backtracking • Tech: Design Pattern
Algorithm
DSA
Backtracking — Permutations (LC 46)
Generate all permutations of an array.
Example
Input: [1,2,3] → Output: all permutations
Where it shows up
State space search, scheduling, puzzle solvers.
References
Low-level design
LLD
ATM System
Requirements
- Authenticate, withdraw, deposit, balance; ATM state & cash bins.
Expectations
- UML for Account, Card, ATM, Transaction; state pattern for ATM.
- Simulate basic flows with validations.
Where it shows up
Bank ATMs; kiosk-based transactional systems.
References
High-level design
HLD
Video Streaming
Requirements
- Upload → transcode → store renditions → stream via HLS/DASH.
Expectations
- Worker pipeline, object storage, CDN, player ABR logic basics.
- Metadata & search index; cost controls.
Where it shows up
YouTube/OTT, education platforms.
References
Today's deep-dive
Tech
Design Pattern
Implement Strategy + Observer around a pricing/notification domain. Unit test swapping strategies without touching clients.
Where it shows up
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