Question 1

How would you design a news feed system?

Accepted Answer

**Target Audience:** Engineers preparing for a senior system design round. You know what a server, a database and a cache are; feed-specific ideas are defined as we go.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Product facts are cited inline and were checked in October 2026.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the words an interviewer expects.

Question 2

How would you design Twitter's timeline at scale?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round. You know what a cache and a database are; the timeline-specific ideas are defined as we go.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Twitter figures are from published talks and write-ups cited inline, checked in October 2026.

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts with the precise vocabulary. The cost table is computed by the

Question 3

How would you design a typeahead/autocomplete system?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round; you know what a server and a database are, and data structures like tries are explained from scratch.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). The capacity figures are worked arithmetic from stated assumptions, not measurements of a real service.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Intervi

Question 4

How would you design Twitter's timeline and search? (Facebook feed)

Accepted Answer

## Step 1: Use Cases, Constraints, Assumptions, Back-of-Envelope

### Use cases
We'll scope to handle only the core flows that expose the bottlenecks; everything else is deferred.

- **User** posts a tweet — 280 chars + media refs, persisted, then fanned out to followers' timelines.
- **User** reads home timeline — GET merged, ranked feed (paginated, <200ms p95).
- **Service** searches tweets — inverted index over tokens/hashtags with ranking and recency.
- **Service** fans out / backfills — asy

Question 5

How would you design Amazon's category sales ranking?

Accepted Answer