Essential Interview Topics Every Developer Should Master

Whether you’re preparing for your next frontend, backend, or full-stack interview, the questions you’ll face tend to fall into three core categories: Data Structures & Algorithms, Machine Coding / Practical Rounds, and System Design. At a certain level, it doesn’t matter which side of the stack you work on. Strong fundamentals always win.

This post is a curated list of the most commonly asked topics across these three areas, along with brief notes on what interviewers are really looking for.

Data Structures & Algorithms

These questions test your ability to think through problems efficiently. Interviewers care about your approach, time/space complexity analysis, and how you handle edge cases.

Caching

• Implement LRU Cache - Use a hashmap + doubly linked list. Know the O(1) get/put contract.
• Implement LFU Cache - Extends LRU with frequency tracking. Multiple data structures working together.

Read the full breakdown with Python implementations: Caching in Interviews - LRU and LFU Cache

Heaps & Priority Queues

• Find Median from Data Stream - Two heaps (max-heap + min-heap) to maintain running median.
• Merge K Sorted Lists - Min-heap or divide-and-conquer. Classic for understanding priority queues.
• Kth Largest Element in a Stream - Min-heap of size K.
• Top K Frequent Elements - Hashmap + heap, or bucket sort for O(n).

Sliding Window & Two Pointers

• Maximum Subarray Sum (Kadane’s + variations) - Foundation of dynamic programming thinking.
• Sliding Window Maximum - Monotonic deque. Tests your understanding of amortized complexity.
• Longest Substring Without Repeating Characters - Classic sliding window with a set/map.
• Minimum Window Substring - Harder sliding window with character frequency matching.

Trees & Graphs

• Lowest Common Ancestor (Binary Tree) - Recursive DFS. Know the difference between BST and BT versions.
• Serialize & Deserialize Binary Tree - BFS or preorder traversal with null markers.
• Number of Islands - BFS/DFS on a grid. Entry point for graph traversal questions.
• Course Schedule (Topological Sort) - Detect cycles + ordering in a DAG. Kahn’s algorithm or DFS.
• Detect Cycle in a Directed Graph - DFS with coloring (white/gray/black) or in-degree tracking.
• Word Ladder - BFS for shortest transformation sequence. Tests graph modeling from strings.

Dynamic Programming

• Coin Change - Classic unbounded knapsack. Understand top-down vs bottom-up approaches.

Design Problems in DSA

• Design a Task Scheduler with Priorities - Combines heaps, greedy algorithms, and cooldown logic.

Machine Coding / Practical Rounds

These rounds test whether you can actually build things. You’ll be judged on code structure, component design, state management, and how you handle edge cases in a time-boxed setting.

Core UI Patterns

• Build a Todo / Task Management App - CRUD operations, state management, filtering. Sounds simple, but clean architecture matters.
• Build a Kanban Board (drag & drop) - Drag events, state transitions between columns, reordering logic.
• Build a Form Builder with Validation - Dynamic field rendering, validation rules, error states.

Data-Heavy UIs

• Build a Search with Autocomplete & Debouncing - API integration, debounce/throttle, keyboard navigation, caching results.
• Build a Pagination / Infinite Scroll System - Intersection Observer, loading states, cursor vs offset pagination.
• Build a Dashboard with Charts & Filters - Data transformation, filter composition, responsive visualizations.

Real-Time & Interactive

• Build a Real-time Chat UI - WebSocket handling, message ordering, optimistic updates, scroll anchoring.
• Build a Notification / Toast System - Queue management, auto-dismiss timers, stacking behavior, accessibility.
• Build a Calendar / Scheduler Application - Date math, recurring events, drag-to-resize, timezone handling.

System-Level UI

• Build a File Explorer (like VS Code) - Recursive tree rendering, lazy loading, context menus, keyboard shortcuts.
• Build a Shopping Cart with Checkout Flow - Multi-step forms, price calculation, inventory validation.
• Build a Feature Flag / Toggle System - Configuration-driven rendering, environment awareness, override logic.

System Design

System design interviews test your ability to think at scale. You’re expected to discuss trade-offs, identify bottlenecks, and reason about distributed systems, even if you’ve never built one at that scale.

Messaging & Real-Time

• Design a Scalable Chat Application (WhatsApp/Slack) - WebSockets vs long polling, message queues, presence system, E2E encryption considerations.
• Design a Notification System (Email/SMS/Push) - Fan-out strategies, priority queues, delivery guarantees, template management.

Data & Storage

• Design a URL Shortener (Bitly/TinyURL) - Hashing strategies, base62 encoding, read-heavy optimization, analytics tracking.
• Design a Distributed Cache System - Consistent hashing, eviction policies, cache invalidation, replication.
• Design a File Storage System (Google Drive) - Chunked uploads, deduplication, sync conflicts, access control.

Rate Limiting & Infrastructure

• Design an API Rate Limiter - Token bucket, sliding window, distributed rate limiting across nodes.
• Design a Logging & Monitoring System - Log aggregation, time-series databases, alerting pipelines, sampling strategies.
• Design a Metrics & Analytics Platform - Event ingestion, real-time vs batch processing, dashboards, data warehousing.

Consumer Products

• Design a Ride-Hailing System (Uber/Ola) - Geospatial indexing, matching algorithms, surge pricing, ETA calculation.
• Design a Video Streaming Platform (YouTube/Netflix) - CDN architecture, adaptive bitrate streaming, recommendation engine, content processing pipeline.
• Design a Payment Gateway (Stripe/Razorpay) - Idempotency, transaction states, reconciliation, PCI compliance considerations.
• Design a News Feed System - Fan-out on write vs read, ranking algorithms, content moderation, caching layers.

E-Commerce & Scheduling

• Design an E-commerce Checkout System - Inventory reservation, payment orchestration, order state machine, cart expiry.
• Design a Leaderboard System - Sorted sets, real-time updates, partitioning strategies, tie-breaking.
• Design a Distributed Job Scheduler - Task queues, retry logic, dead-letter queues, cron-like scheduling at scale.
• Design a Feature Flag System - Gradual rollouts, A/B testing integration, targeting rules, kill switches.
• Design a Search Autocomplete System - Trie data structures, ranking by popularity, prefix matching, personalization.

How to Use This List

1. Don’t just read, implement. Pick one topic per day and actually code it or whiteboard it.
2. Focus on trade-offs. Every solution has compromises. Be ready to discuss why you chose approach A over B.
3. Practice explaining out loud. Interviews are conversations, not exams. Your thought process matters as much as the final answer.
4. Go deep on a few, not shallow on all. It’s better to truly understand 10 problems than to have surface-level familiarity with 50.

Frontend or backend, it doesn’t matter at this level. Strong fundamentals always do.