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LLDCoding - Master LLD and Concurrency

LLDCoding - Master LLD and Concurrency

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Designing a Like / Reaction System (Facebook / LinkedIn) - Database Modelling

Subhahu Jain

Jan 19, 2026 4 min read

Modern platforms (Reddit, LinkedIn, YouTube) support multiple reaction types per entity. Core Requirements ✅ One user → one reaction per entity ✅...

Designing a Like / Reaction System (Facebook / LinkedIn) - Database Modelling

📘 Why Indexes Are Not Free

Subhahu Jain

Jan 18, 2026 3 min read

The Silent Cost Behind Fast Reads Indexes don’t make systems faster —they shift cost from reads to writes, memory, and latency tails. 🧠 The...

📘 Why Indexes Are Not Free

🎤 Live Podcast with Guests — Concurrency Problem

Subhahu Jain

Jan 17, 2026 4 min read

🧠 Real-World Scenario You’re building a live podcast platform where: A host starts a live podcast session. Multiple guests are invited to...

🎤 Live Podcast with Guests — Concurrency Problem

[Uber] Design 🏢(LLD) Meeting Scheduler - Machine Coding Interview

Subhahu Jain

Nov 9, 2025 4 min read

We are designing a meeting scheduler with the following requirements: There are N rooms. We are given a stream of meeting requests (start time, end...

[Uber] Design 🏢(LLD) Meeting Scheduler - Machine Coding Interview

Multi-Threaded Parentheses Validator

Subhahu Jain

Sep 20, 2025 3 min read

Problem: Parallel Parentheses Validator Description You are given a string s of length N consisting only of the characters '(' and ')'. A parentheses...

Multi-Threaded Parentheses Validator

Design (LLD) Paytm/Phone Wallet System - Machine Coding

Subhahu Jain

Sep 4, 2025 4 min read

Asked in Phonepe interview. Design and implement a Paytm/PhonePe Wallet System that supports multiple concurrent users performing transactions at the...

Design (LLD) Paytm/Phone Wallet System - Machine Coding