6 min read Dijkstra’s Algorithm – Shortest Path (Non-negative Weights) import heapq from collections import defaultdict def dijkstra(graph: dict, start: int, n: int) […] Read article
5 min read Requirements and Scale Functional: shorten long URLs, redirect short URLs to originals, track click analytics (count, geography, device, referrer), support Read article
5 min read Core Entities Survey: survey_id, creator_id, title, description, status (DRAFT, ACTIVE, PAUSED, CLOSED), settings (JSONB: allow_anonymous, one_response_per_user, show_progress_bar, randomize_questions, response_limit), start_date, Read article
4 min read Heap Fundamentals A heap is a complete binary tree where every parent satisfies the heap property (min-heap: parent = children). Read article
4 min read GCD, LCM, and Euclidean Algorithm import math def gcd(a: int, b: int) -> int: while b: a, b = b, Read article
7 min read Core Entities Poll: poll_id, creator_id, question, poll_type (SINGLE_CHOICE, MULTIPLE_CHOICE, RANKED, RATING), status (DRAFT, ACTIVE, CLOSED), is_anonymous, allow_change_vote, visibility (PUBLIC, PRIVATE, Read article
5 min read String Fundamentals for Interviews Strings are immutable in Python and Java — concatenating in a loop is O(n^2). Use a Read article
6 min read Recursion Fundamentals Every recursive solution has: a base case (stops the recursion), a recursive case (reduces the problem), and a Read article
7 min read Core Entities Cart: cart_id, user_id (NULL for guest), session_id (for guest carts), status (ACTIVE, ABANDONED, CHECKED_OUT), currency, created_at, updated_at, expires_at. Read article
6 min read Geospatial Data Fundamentals Geospatial queries are common in production systems: “find the 10 nearest restaurants,” “is this user inside a Read article
7 min read Trie Fundamentals and Implementation A trie (prefix tree) stores strings character by character, sharing prefixes among strings. Each node represents Read article
6 min read Core Entities Home: home_id, owner_id, name, address, timezone, created_at. Room: room_id, home_id, name, floor_number. Device: device_id, home_id, room_id, name, type Read article
6 min read Binary Search Fundamentals Binary search finds a target in a sorted collection in O(log n). The key insight: at each Read article
6 min read Why Distributed Caching? A single application server’s in-memory cache is lost on restart and not shared across instances. A distributed Read article
6 min read Core Entities Tenant: tenant_id, name, slug, plan, custom_domain, storage_quota_gb, created_at. (Multi-tenant: each customer organization is a tenant with isolated content.) Read article
