Algorithmic Thinking Patterns

System Design Prerequisites You Should Always Consider

System Design: Booking. com / Hotel Booking System

DSA Interview Essentials – Must-Know Questions Table

When to Use HTTP Methods. 1) GET – When you're asking for data. - Example: Fetch a user profile.- No side effects, no body usually. 2) POST – When you're creating something new. - Example: Submit a form, register a user.- Can change server state. 3) PUT – When you're replacing.

Docker - All You Need to Know

Which One Would You Pick in an Interview?

(Hint: Use scheduled fan-out, batching, and rate-limited retry queues.).

You release a new feature and want to notify all users. You push to 5M devices at once. Firebase throttles, your queue overloads, and some users get no notification. How to handle this?.

Small files → Direct or streaming. Large/static files → Pre-signed URLs or CDN. Heavy exports → Async + polling.

Different Ways to Handle File Downloads ⬇️. 1. Direct Download (Synchronous). - API reads file → returns it as response.👍 Simple to implement.👎 Blocks server thread, bad for large files. 2. Streaming Download.- Reads file in chunks, writes to response stream.👍 Low memory.

(Hint: Dead-letter queues, per-job timeouts, retries with isolation).

You enqueue 10,000 emails for sending via a worker queue. A bug in one message blocks the entire queue from progressing. How do you design the system to be fault-tolerant and allow processing to continue despite bad jobs?.

Some Famous NP Problems. ✅NP-Complete : (Hard to solve, easy to verify) 👇. 1) SAT (Boolean Satisfiability) – Can you make a logic formula true by assigning values to variables?. 2) 3-SAT – Same as SAT but each clause has exactly 3 variables. 3) Subset Sum – Is there a subset.

How Sessions and Cookies Work Together. 1. User visits your site and logs in. They send a POST request with their username and password. 2. Server checks credentials and creates a session. - A session is a record stored on the server (usually in memory, Redis, or a DB). - It.

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Different Ways to Serialize Data. 1) JSON. Text-based, human-readable.👍 Universally supported, easy to debug.👎 Verbose, slow to parse at scale. 2) XML. Hierarchical, schema-support.👍 Good for enterprise/data contracts.👎 Heavy, noisy syntax. 3) Protocol Buffers (Protobuf).

Redis - All You Need to Know

Widely-used Python libraries simplfied

Over-logging can be dangerous. It slows you down, drowns real issues, and eats infra costs. Logging is like salt in cooking - essential, but easy to overdo. Before adding a log line, ask:. • Who will read this and why?.• Is there a cheaper way to get this info?.• Will this.