Interview Experience – Senior Backend / Ads / Distributed Systems (5 Rounds) --- ## 🔹

Round 1 Coding + Ads Fundamentals

Focus Areas: - Project

deep dive 3–4 behavioral questions - Complete A

Interview Experience – Senior Backend / Ads / Distributed Systems (5 Rounds) --- ## 🔹

Round 1 Coding + Ads Fundamentals

Focus Areas: - Project

deep dive 3–4 behavioral questions - Complete Ads ecosystem explanation - Advertiser → DSP → Ad Exchange → SSP → Publisher - Real-time bidding (RTB) flow - Ranking & auction basics - End-to-end ad serving lifecycle

Coding Question: - Map of Map encoding problem - Required graph search - Implemented, executed, and discussed optimizations --- ## 🔹

Round 2 Ads HLD + Search + ML ### 1️⃣ Design HLD for Microsoft Bing Ads Designed high-level architecture similar to Microsoft Bing Ads.

Covered: - Campaign setup & management - Budget pacing - Ranking logic & quality score - Auction mechanism - Publisher integration via SSP - End-to-end ads delivery flow --- ### 2️⃣ Search API Design

Problem: Design an API for: “Plumbers near Kondapur”

Discussion Points: - Data ingestion pipeline - Indexing (inverted index + geo-spatial indexing) - Semantic matching - Hybrid retrieval (BM25 + embeddings) - Ranking signals & personalization --- ### 3️⃣ ML & LLM Discussion - Random Forest vs SVM - RAG (Retrieval-Augmented Generation) with LLMs - Trade-offs: classical ML vs LLM-based systems - Agentic frameworks for automation in ads optimization --- ## 🔹

Round 3 Payment System Design (Razorpay-like) Designed a payment gateway system similar to Razorpay.

Covered: ### Payment Flow - App → Gateway → Bank - OTP handling - 3DS flow - Callback/webhook handling ### Reliability & Safety - Idempotency keys - Retry mechanisms - Handling bank timeouts - Double debit protection ### System Concerns - DDoS protection - Fraud detection - Rate limiting - Observability ### Integration & UX - Integration across app, gateway, and bank APIs - Localization & language support - UI rendering based on user country/currency --- ## 🔹

Round 4 Hiring Manager + Bar Raiser (Onsite) ###

System Design Website Activity Analytics

Requirement: - Track clicks/actions/users - 18-month lookback - 5-minute granularity - Filter by language, country, and other attributes

Discussion Points: - Event-based schema (fact + dimension tables) - SQL vs Time-Series DB - Partitioning strategy & pruning - Logged-in vs logged-out user tracking - Data pipelines & SLAs ### Advanced Topics - Bloom Filters - Count-Min Sketch - Hashing in Redis - Sampling & standard deviation use cases - Transformer architecture basics - Effect of Temperature, Top-K, Top-P on LLM outputs - AI tool adoption metrics & measuring agentic AI impact --- ## 🔹

Round 5 (LLD) - Onsite ### Coding on Whiteboard - LRU Cache (write code on board) ### System & Behavioral Discussion - Eviction strategies - Caching trade-offs - Reason for leaving - Leadership & conflict handling - Notice period expectations